The Web Animations Level 2 spec moved from `double?` to `CSSNumberish?` for the startTime and currentTime Animation attributes.
Pull request: https://github.com/WebKit/WebKit/pull/5641
Submitted web-platform-tests pull request: https://github.com/web-platform-tests/wpt/pull/36599
Committed 255870@main (4dc7e1ab89bb): <https://commits.webkit.org/255870@main> Reviewed commits have been landed. Closing PR #5641 and removing active labels.
<rdar://problem/101457576>