We should remove WebKitWebContext:use-system-appearance-for-scrollbars from the GTK 4 API because system appearance is not supported with GTK 4.
It's already #if-ed out for GTK4, except for the header.
Pull request: https://github.com/WebKit/WebKit/pull/9408
And there is no GObject property WebKitWebContext:use-system-appearance-for-scrollbars anyway
Committed 259716@main (c2e9b5aaac76): <https://commits.webkit.org/259716@main> Reviewed commits have been landed. Closing PR #9408 and removing active labels.