Warning instead of exception on unsupported Ubuntu

[sagudev]

For someone who is always using latest stable Ubuntu version it is pretty annoying to change the script every time, so issuing a warning instead of error would still allow users on unsupported version to continue bootstrapping.

---

• ./mach build -d does not report any errors
• ./mach test-tidy does not report any errors
• These changes fix #___ (GitHub issue number if applicable)

• There are tests for these changes OR
• These changes do not require tests because changes are in bootstrap script

[jdm]

@bors-servo r+

[bors-servo]

📌 Commit 73bd128 has been approved by jdm

[bors-servo]

⌛ Testing commit 73bd128 with merge f7e8866...

[github-actions]

Results from try job (#4204089803):

Unexpected results that are known to be intermittent (39)

• OK [expected TIMEOUT] /FileAPI/url/url-charset.window.html (#26997)
  • PASS [expected TIMEOUT] subtest: Blob charset should override any auto-detected charset.
  • PASS [expected TIMEOUT] subtest: Blob charset should override <meta charset>.
• TIMEOUT /FileAPI/url/url-in-tags-revoke.window.html (#19978)
  • FAIL [expected TIMEOUT] subtest: Opening a blob URL in a new window immediately before revoking it works.
• OK /_mozilla/mozilla/scrollBy.html (#21321)
  • FAIL [expected PASS] subtest: Ensure that the window.scrollBy function affects scroll position as expected
• OK /css/CSS2/floats/hit-test-floats-002.html (#25733)
  • PASS [expected FAIL] subtest: Hit test float
• OK /css/CSS2/floats/hit-test-floats-004.html (#25804)
  • FAIL [expected PASS] subtest: Miss float below something else
• OK /css/CSS2/normal-flow/block-in-inline-hittest-001.html (#29064)
  • FAIL [expected PASS] subtest: block-in-inline-hittest-001
• OK /css/CSS2/normal-flow/block-in-inline-hittest-002.html (#29057)
  • PASS [expected FAIL] subtest: elementFromPoint
• OK /css/CSS2/normal-flow/block-in-inline-hittest-float-002.html (#29051)
  • FAIL [expected PASS] subtest: block-in-inline-hittest-float-002
• OK /css/CSS2/normal-flow/hit-test-anonymous-block.html (#25807)
  • FAIL [expected PASS] subtest: Hit test beside line of text inside anonymous block
• PASS [expected TIMEOUT] /css/CSS2/selectors/attribute-value-selector-004.xht
• OK /css/css-flexbox/hittest-before-pseudo.html (#26521)
  • PASS [expected FAIL] subtest: Hit-testing text within a pseudo-element flex-item should return the flexbox as the hittest result.
• OK /css/css-fonts/variations/at-font-face-font-matching.html (#20684)
  • PASS [expected FAIL] subtest: Matching font-weight: '399' should prefer '200 300' over '400'
  • FAIL [expected PASS] subtest: Matching font-stretch: '100%' should prefer '100%' over '110% 120%'
  • PASS [expected FAIL] subtest: Matching font-stretch: '110%' should prefer '110% 120%' over '115% 116%'
  • PASS [expected FAIL] subtest: Matching font-stretch: '110%' should prefer '105%' over '100%'
  • FAIL [expected PASS] subtest: Matching font-style: 'normal' should prefer 'oblique 20deg 30deg' over 'oblique -50deg -20deg'
  • FAIL [expected PASS] subtest: Matching font-style: 'italic' should prefer 'oblique 5deg 10deg' over 'oblique 5deg'
  • PASS [expected FAIL] subtest: Matching font-style: 'oblique 20deg' should prefer 'oblique 10deg' over 'italic'
  • PASS [expected FAIL] subtest: Matching font-style: 'oblique 21deg' should prefer 'oblique -50deg -20deg' over 'oblique -40deg -30deg'
  • FAIL [expected PASS] subtest: Matching font-style: 'oblique 10deg' should prefer 'oblique 10deg' over 'oblique 5deg'
  • FAIL [expected PASS] subtest: Matching font-style: 'oblique -21deg' should prefer 'italic' over 'oblique 0deg'
• OK /css/cssom-view/elementFromPoint-float-in-relative.html (#27753)
  • FAIL [expected PASS] subtest: elementFromPoint-float-in-relative
• OK /css/cssom-view/elementFromPoint-list-001.html (#23915)
  • FAIL [expected PASS] subtest: <li>Inside 2</li>
  • FAIL [expected PASS] subtest: <li>Image Inside 1</li>
• OK /css/cssom-view/elementFromPoint-subpixel.html (#23623)
  • FAIL [expected PASS] subtest: Hit test top left corner of box
• OK /css/cssom-view/elementFromPoint-visibility-hidden-resizer.html (#28695)
  • PASS [expected FAIL] subtest: elementFromPoint on resizer area of an element with visibility:hidden
• TIMEOUT /fetch/metadata/generated/css-images.sub.tentative.html (#29047)
  • PASS [expected TIMEOUT] subtest: background-image sec-fetch-site - HTTPS downgrade (header not sent)
• TIMEOUT [expected OK] /fetch/private-network-access/iframe.tentative.https.window.html (#29091)
  • TIMEOUT [expected FAIL] subtest: public to local, grandparent navigates: failure.
  • TIMEOUT [expected FAIL] subtest: public to local, grandparent navigates: success.
• TIMEOUT [expected ERROR] /html/browsers/browsing-the-web/history-traversal/persisted-user-state-restoration/scroll-restoration-fragment-scrolling-cross-origin.html (#28541)
• OK [expected TIMEOUT] /html/browsers/browsing-the-web/navigating-across-documents/005.html (#27062)
• OK [expected TIMEOUT] /html/browsers/browsing-the-web/navigating-across-documents/initial-empty-document/iframe-src-aboutblank-navigate-immediately.html (#29048)
  • PASS [expected TIMEOUT] subtest: Navigating to a different document with form submission
• OK /html/browsers/browsing-the-web/navigating-across-documents/initial-empty-document/load-pageshow-events-iframe-contentWindow.html (#28681)
  • FAIL [expected PASS] subtest: load & pageshow events do not fire on contentWindow of <iframe> element created with src='about:blank'
• TIMEOUT [expected OK] /html/browsers/browsing-the-web/navigating-across-documents/javascript-url-load-as-html.xhtml (#29070)
  • TIMEOUT [expected PASS] subtest: javascript: URL navigation to a string must create a HTML document using the correct properties
• OK /html/browsers/browsing-the-web/navigating-across-documents/navigation-unload-same-origin.window.html (#29049)
  • PASS [expected FAIL] subtest: Same-origin navigation started from unload handler must be ignored
• OK /html/browsers/history/the-history-interface/traverse_the_history_5.html (#21383)
  • PASS [expected FAIL] subtest: Multiple history traversals, last would be aborted
• OK /html/browsers/the-window-object/open-close/creating_browsing_context_test_01.html (#29046)
  • PASS [expected FAIL] subtest: first argument: absolute url
• OK [expected TIMEOUT] /html/interaction/focus/the-autofocus-attribute/update-the-rendering.html (#24145)
  • FAIL [expected TIMEOUT] subtest: "Flush autofocus candidates" should be happen before a scroll event and animation frame callbacks
• OK [expected CRASH] /html/semantics/embedded-content/the-iframe-element/iframe_sandbox_popups_nonescaping-1.html (#24066)
• TIMEOUT [expected OK] /html/semantics/embedded-content/the-iframe-element/iframe_sandbox_popups_nonescaping-2.html (#22154)
  • NOTRUN [expected FAIL] subtest: Check that popups from a sandboxed iframe do not escape the sandbox
• OK [expected TIMEOUT] /html/semantics/links/links-created-by-a-and-area-elements/htmlanchorelement_noopener.html (#23205)
  • PASS [expected NOTRUN] subtest: Check that rel=noopener with target=_self does a normal load
• ERROR [expected OK] /html/semantics/scripting-1/the-script-element/defer-script/async-script.html?reload (#29054)
• OK /html/webappapis/dynamic-markup-insertion/document-write/module-delayed.html (#27659)
  • PASS [expected FAIL] subtest: async document.write in a module
• OK /html/webappapis/dynamic-markup-insertion/document-write/module-static-import-delayed.html (#26243)
  • FAIL [expected PASS] subtest: document.write in an imported module
• TIMEOUT [expected OK] /html/webappapis/scripting/processing-model-2/unhandled-promise-rejections/promise-rejection-events.html (#26371)
  • TIMEOUT [expected FAIL] subtest: delayed handling: delaying handling rejected promise created from createImageBitmap will cause both events to fire
• OK [expected TIMEOUT] /webaudio/the-audio-api/the-audiocontext-interface/audiocontext-not-fully-active.html (#27664)
• CRASH [expected TIMEOUT] /webmessaging/broadcastchannel/cross-partition.https.tentative.html (#29058)
• OK [expected TIMEOUT] /webmessaging/without-ports/017.html (#24486)
  • PASS [expected TIMEOUT] subtest: origin of the script that invoked the method, about:blank
• TIMEOUT [expected OK] /webmessaging/without-ports/018.html (#24485)
  • TIMEOUT [expected PASS] subtest: origin of the script that invoked the method, javascript:
• OK [expected ERROR] /workers/constructors/Worker/Worker-constructor.html (#22991)

[bors-servo]

☀️ Test successful - checks-github
Approved by: jdm
Pushing f7e8866 to master...

[sagudev]

Results from try job (#4204089803):
Unexpected results that are known to be intermittent (39)

It would be more stylish to create results from @bors-servo instead of github-actions bot, but that is just my nitpicking.