Mark flaky test accessibility/aom-click-action.html as Timeout

The test has been flaky on all platforms:
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=blink_web_tests%20(with%20patch)&tests=accessibility/aom-click-action.html

TBR=aboxhall@chromium.org
NOTRY=True

Bug: 1134459
Change-Id: I795f7a7b21eef84a24d5b56e42240604e863ff8e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2559375Reviewed-by: Yi Gu <yigu@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830747}

third_party/blink/web_tests/TestExpectations

@@ -6029,4 +6029,5 @@ crbug.com/1087242 http/tests/inspector-protocol/service-worker/network-extrainfo
 crbug.com/1149771 [ Linux ] virtual/android/fullscreen/video-scrolled-iframe.html [ Pass Timeout ]
 crbug.com/1152532 http/tests/devtools/service-workers/user-agent-override.js [ Pass Timeout ]
 crbug.com/1092048 external/wpt/FileAPI/blob/Blob-stream.any.html [ Pass Timeout ]
-crbug.com/1092048 external/wpt/FileAPI/blob/Blob-stream.any.worker.html [ Pass Timeout ]
+crbug.com/1092048 external/wpt/FileAPI/blob/Blob-stream.any.worker.html [ Pass Timeout ]
\ No newline at end of file
+crbug.com/1134459 accessibility/aom-click-action.html [ Pass Timeout ]