Avoid terminating from another thread in some thread termination
unit tests.

Change-Id: I0f66e49f1f4e7e3d6ec4c614c2cc1afc9fdb0a22
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3816663
Commit-Queue: Qifan Pan <panq@google.com>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82284}