Some site isolation interaction tests had postMessage sent on the load of the iframe instead of when the event was firing.
<rdar://problem/118436235>
Pull request: https://github.com/WebKit/WebKit/pull/20522
Committed 270759@main (fa7308e615b9): <https://commits.webkit.org/270759@main> Reviewed commits have been landed. Closing PR #20522 and removing active labels.