Concurrent allocation test was failing flakily. Do not fix this simply
by increasing heap size since this would reduce frequency of GCs.
Instead allow allocations to fail. Even in this case the allocation
code path is still executed which we want to test.

Bug: v8:11084, v8:10315
Change-Id: I0daa9ad9177aab8b02b7decf2ccfd50e0d8ab9b6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2516471Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70946}