Triage css-background tests
Also fix reference and spec links in background-clip:text test.
Bug: 329302543, 362055819
Change-Id: I4267efb513c6a51182b0d2b5211924ffbcd05a0c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5811983
Reviewed-by: Steinar H Gunderson sesse@chromium.org
Commit-Queue: Rune Lillesveen futhark@chromium.org
Cr-Commit-Position: refs/heads/main@{#1346672}