Automatic update from web-platform-tests [css-mixins] Split tests into subdirectories for functions and mixins No changes to the test files other than updating relative paths. WEB_FEATURES.yml files were updated to match all files in respective subdirectories. Bug: 406935599 Change-Id: I864e1ad0bb36a5945fd9945365933b3697d3f764 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/8061706 Reviewed-by: Alison Maher <almaher@microsoft.com> Commit-Queue: Kevin Babbitt <kbabbitt@microsoft.com> Cr-Commit-Position: refs/heads/main@{#1659001} -- wpt-commits: 5f6046734ece0649fa6f3ad2915ea23ba4d3674a wpt-pr: 61166