Change ReturnFuzzSafe to only return undefined when
--correctness-fuzzer-supressions is on, instead of --fuzzing.

Bug: chromium:1200724, v8:11701
Change-Id: I21aa77db89fe26308881985055b023a5c03c2518
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2905593
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Auto-Submit: Patrick Thier <pthier@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74671}