[Sheriff] Disable flaky test AccessibilityFencedFrameScrollable

Test failing on builder chrome/ci/linux-chromeos-chrome.

Bug: 1428918
AX-Relnotes: n/a.
Change-Id: I233a4eea6c459234d60fbb4659ae1ae4fe717ea9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4381249


Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Auto-Submit: thefrog <thefrog@chromium.org>
Owners-Override: Dale Curtis <dalecurtis@chromium.org>
Commit-Queue: thefrog <thefrog@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1123741}