Test fails flakily with concurrent allocation. The test checks
heap size after GC, therefore simply disable concurrent allocation.

Bug: v8:10315
Change-Id: If0b7a5c12f23322f992c0c9568f7d3aa81f4a245
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2418715Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70016}