When starting incremental marking from an allocation observer, the
DCHECK for AllowGarbageCollection::IsAllowed() fails. We need to
explicitly allow this here in order to use SafepointScope.

Bug: chromium:1271659, v8:11708, v8:12413
Change-Id: I8607a82faed50f8dfffce1e495fb5e715a47bc1b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3293086
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Auto-Submit: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77996}