The first build with the failure that I see is https://build.webkit.org/#/builders/434/builds/79
Running Layout/nested-flexbox.html (163 of 210)
Finished: 5.304282 s
Actually, build 79 is just the first completed build on this queue, and looking at Gtk, I see that the test has been failing for longer.
Perhaps it was landed broken?
I have skipped this test while this issue is investigated.
Pull request: https://github.com/WebKit/WebKit/pull/1732
Test gardening commit 251791@main (f1c3b0288188): <https://commits.webkit.org/251791@main>
Reviewed commits have been landed. Closing PR #1732 and removing active labels.