[test] Disable --stress-concurrent-allocation with TestSizeOfObjects

This test checks SizeOfObjects after GC, but there might be concurrent
allocations in-between.

Bug: v8:10315
Change-Id: Id904c8865e44ac5c3b486ff6f1316e536cf20e9f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2428864Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70122}

test/cctest/heap/test-heap.cc

@@ -1693,6 +1693,7 @@ TEST(TestSizeOfRegExpCode) {
 
 
 HEAP_TEST(TestSizeOfObjects) {
+  FLAG_stress_concurrent_allocation = false;
   v8::V8::Initialize();
   Isolate* isolate = CcTest::i_isolate();
   Heap* heap = CcTest::heap();