Tests aren't compatible with concurrent allocation on background threads.

Bug: v8:10315
Change-Id: I376e98858fa1aacf1689e6791985774299def319
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2418391Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69989}