The fuzzers were passing the flag --es-staging which doesn't exist. This
CL updates them to pass the flag --harmony which does exist.

Change-Id: I02c83026e5b9bdf49e51e700f16702bf56cd49e8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3522064Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79464}