Adjust WATCHLISTS to only send out updates to those testfiles as part
of notifying oilpan-reviews+v8@.

Change-Id: Ib877f0353ea2b2d1ac06c93d450145dbeb6fcc66
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3260517
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77713}