This is a necessary assumption for concurrent marking in MinorMC and
will simplify the code as it allows MinorMC to reuse the same marking
bitmap as full GCs.

Bug: v8:12612
Change-Id: I5e9be45c7d84320721ce7f7578dee1eb972d6f6a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3732933Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81465}