HeapNumbers that are in the shared heap were incorrectly considered
!IsShared().

TBR=jkummerow@chromium.org

Bug: v8:12547
Change-Id: Ie4b9575445d841a7045c947ff4439bf53a22869d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3504085
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Auto-Submit: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79372}