[Test] Disable bytecode flushing in DecideToPretenureDuringCompilation.

The high GC stressing in this tests causes bytecode flushing which breaks some
invariants in the test.

BUG=v8:8629

Change-Id: I7efff098ed4fa96006c8200e174132a6297bd36f
Reviewed-on: https://chromium-review.googlesource.com/c/1394743Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Ross McIlroy <rmcilroy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58541}

test/cctest/test-compiler.cc

@@ -939,6 +939,7 @@ TEST(DecideToPretenureDuringCompilation) {
   FLAG_stress_gc_during_compilation = true;
   FLAG_allow_natives_syntax = true;
   FLAG_allocation_site_pretenuring = true;
+  FLAG_flush_bytecode = false;
 
   // We want to trigger exactly 1 optimization.
   FLAG_use_osr = false;