It should always be UTF-8 per https://drafts.csswg.org/css-values/#url-processing.
<rdar://problem/114889625>
Pull request: https://github.com/WebKit/WebKit/pull/17383
Committed 270169@main (c195704a1cc8): <https://commits.webkit.org/270169@main> Reviewed commits have been landed. Closing PR #17383 and removing active labels.