code_coverage: avoid spending too much time on flaky fuzzers

This is a simple fix to avoid spending too much time on fuzzers known
to be sometimes flaky, such as the webidl_in_process_fuzzer or the
mojo_js_in_process_fuzzer.

Change-Id: I24e3911ef5dd908b53740ee13060e1b55341e508
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6448893
Reviewed-by: Ali Hijazi <ahijazi@chromium.org>
Auto-Submit: Paul Semel <paulsemel@chromium.org>
Commit-Queue: Paul Semel <paulsemel@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1445794}
NOKEYCHECK=True
GitOrigin-RevId: bd54c00c743947daec81c9bc3cf140d6ad6e050c