8302879: doc/building.md update link to jtreg builds

[gdams]

The Eclipse Adoptium project recently moved its CI from ci.adoptopenjdk.net to ci.adoptium.net. The link to jtreg builds needs updating

Backport is clean (except for a differing format in the HTML version)

See adoptium/infrastructure#2932 for more context

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Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8302879: doc/building.md update link to jtreg builds

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk19u pull/107/head:pull/107
$ git checkout pull/107

Update a local copy of the PR:
$ git checkout pull/107
$ git pull https://git.openjdk.org/jdk19u pull/107/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 107

View PR using the GUI difftool:
$ git pr show -t 107

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk19u/pull/107.diff

[bridgekeeper]

👋 Welcome back gdams! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

This backport pull request has now been updated with issue from the original commit.

[mlbridge]

Webrevs

• 00: Full (539992ea)

[RealCLanger]

JDK19 is dead. You should probably do this in jdk20u 😉

[gdams]

JDK19 is dead. You should probably do this in jdk20u 😉

Yes my bad haha