If processing the marking worklists found new ephemeron pairs, but
processing the existing ephemeron pairs didn't mark new objects, marking
would stop and the newly discovered ephemeron pairs would not be
processed. This can lead to a marked key with an unmarked value.

Bug: chromium:1252878
Change-Id: I0f158f6f64490f1f06961520b4ba57fa204bd867
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3199872
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77197}