The concurrent marker consults the page flags to see if it should skip
objects in the shared heap, and it was missing a SynchronizePageAccess,
causing TSAN false positives.

Bug: v8:12314, v8:12007
Change-Id: I888a68a3eddaa3dfa1644364226010def8d2a9b6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3219946
Auto-Submit: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77390}