If a fork doesn't have the branch a contributor is making a PR against, our API call (and the optimization in https://bugs.webkit.org/show_bug.cgi?id=243283 generally) will fail.
<rdar://problem/108565576>
Pull request: https://github.com/WebKit/WebKit/pull/13201
Committed 263431@main (2a1e05db9254): <https://commits.webkit.org/263431@main> Reviewed commits have been landed. Closing PR #13201 and removing active labels.