Intermittent failure in /eventsource/format-field-retry.htm, /eventsource/format-field-retry-bogus.htm

[jdm]

  ▶ Unexpected subtest result in /eventsource/format-field-retry.htm:
  │ FAIL [expected PASS] EventSource: "retry" field
  │   → assert_true: expected true got false
  │ 
  │ source.onopen/<@http://web-platform.test:8000/eventsource/format-field-retry.htm:24:26
  │ Test.prototype.step@http://web-platform.test:8000/resources/testharness.js:1977:25
  └ source.onopen@http://web-platform.test:8000/eventsource/format-field-retry.htm:19:16
  ▶ Unexpected subtest result in /eventsource/format-field-retry-bogus.htm:
  │ FAIL [expected PASS] EventSource: "retry" field (bogus)
  │   → assert_true: expected true got false
  │ 
  │ source.onopen/<@http://web-platform.test:8000/eventsource/format-field-retry-bogus.htm:23:26
  │ Test.prototype.step@http://web-platform.test:8000/resources/testharness.js:1977:25
  └ source.onopen@http://web-platform.test:8000/eventsource/format-field-retry-bogus.htm:18:16

This is a time-based check at https://github.com/web-platform-tests/wpt/blob/62fcfd1be978d525b68d7d130bbdbd5ab10dcb74/eventsource/format-field-retry.htm#L24, so maybe we sometimes fail it when there are a bunch of tests running simultaneously.