Marking verification should only process young generation objects when
verifying the marking state of a young generation garbage collection.

Bug: v8:12324
Change-Id: I01db261437ec5c42ddb6c79c44e31b5fe0e536d7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3231343Reviewed-by: Omer Katz <omerkatz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77518}