Syncing wpt PR 44531 found new untriaged test failures in CI

Tests Affected

Firefox-only failures

• /css/css-borders/border-image-width-interpolation-math-functions-tentative.html [wpt.fyi]
  • CSS Transitions: property <border-image-width> from [100] to [calc(sign(20rem - 20px) * 180)] at (0) should be [100]: FAIL
  • CSS Transitions with transition: all: property <border-image-width> from [100] to [calc(sign(20rem - 20px) * 180)] at (0) should be [100]: FAIL
  • CSS Animations: property <border-image-width> from [100] to [calc(sign(20rem - 20px) * 180)] at (0) should be [100]: FAIL
  • Web Animations: property <border-image-width> from [100] to [calc(sign(20rem - 20px) * 180)] at (0) should be [100]: FAIL

CI Results

Missing results from treeherder
GitHub PR Head

Notes

These updates will be on mozilla-central once bug 1879849 lands.

Note: this bug is for tracking fixing the issues and is not
owned by the wpt sync bot.

This bug is linked to the relevant tests by an annotation in
https://github.com/web-platform-tests/wpt-metadata. These annotations
can be edited using the wpt interop dashboard
https://jgraham.github.io/wptdash/

If this bug is split into multiple bugs, please also update the
annotations, otherwise we are unable to track which wpt issues are
already triaged. Resolving as duplicate or closing this issue should
be cause the bot to automatically update or remove the annotation.

This looks the same as bug 1879882 (interpolation using sign() expressions in one of the values); just with lengths here, rather than angles. --> Adding see-also.