[TSan] Unlock fastpath when checking domains_to_finalize (#5598)

[TSan] Unlock fastpath when checking domains_to_finalize (#5598)

[TSan] Unlock fastpath when checking domains_to_finalize

I understand that the affected line is a fastpath which seems absolutely fine to me as it is properly checked later. It is, however, rightfully, detected as a data race by Clang's ThreadSanitizer. I would, therefore, suggest using `UnlockedReadPointer ()` to mark this race as known + accepted.