[test] Add --stress-flush-code to numfuzz experiments

No-Try: true
Bug: v8:12172
Change-Id: I4bace3c91e71e4529ac8d75df3297036c6ca9756
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3141588
Auto-Submit: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76687}

tools/testrunner/testproc/fuzzer.py

@@ -44,6 +44,7 @@ EXTRA_FLAGS = [
   (0.1, '--regexp-tier-up-ticks=100'),
   (0.1, '--stress-background-compile'),
   (0.1, '--stress-concurrent-inlining'),
+  (0.1, '--stress-flush-code'),
   (0.1, '--stress-lazy-source-positions'),
   (0.1, '--stress-wasm-code-gc'),
   (0.1, '--turbo-instruction-scheduling'),