Download::platformCancelNetworkLoad() may call its completion handler on the wrong thread, leading to crashes in the Timer destructor because the Download object gets destroyed off the main thread.
<rdar://74650424>
Pull request: https://github.com/WebKit/WebKit/pull/1837
Committed 251897@main (ac21d7522331): <https://commits.webkit.org/251897@main> Reviewed commits have been landed. Closing PR #1837 and removing active labels.