[heap] Disable --stress-concurrent-allocation for test

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}

test/cctest/test-api.cc

@@ -7661,7 +7661,7 @@ static void SetFlag(const v8::WeakCallbackInfo<FlagAndPersistent>& data) {
 }
 
 static void IndependentWeakHandle(bool global_gc, bool interlinked) {
-  i::FLAG_stress_incremental_marking = false;
+  ManualGCScope manual_gc_scope;
   // Parallel scavenge introduces too much fragmentation.
   i::FLAG_parallel_scavenge = false;
   v8::Isolate* iso = CcTest::isolate();