Disable TestMouseOverShownMenu.

It's been flaky on several platform,
bug is already open for fixing it.

Bug: 40765889
Change-Id: I0f6a06d81a2ce45b60fae471d9f962862cbd5f77
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5405305


Reviewed-by: thefrog <thefrog@chromium.org>
Commit-Queue: Noam Rosenthal <nrosenthal@chromium.org>
Owners-Override: Noam Rosenthal <nrosenthal@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1280210}