[sheriff] Disable flaky web test

http/tests/websocket/multiple-connections-throttled.html is flaky on
every platform. See bug for details.

Bug: 1167222
Change-Id: Ia3b28cbc716da45b098877c2677a4c319fad9e64
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2633089
Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Reviewed-by: Yi Gu <yigu@chromium.org>
Auto-Submit: Fabrice de Gans-Riberi <fdegans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844151}

third_party/blink/web_tests/TestExpectations

@@ -5882,3 +5882,4 @@ crbug.com/1060837 virtual/plz-dedicated-worker/external/wpt/html/cross-origin-em
 
 # Sheriff 2021-01-15
 crbug.com/1167210 [ Mac ] virtual/forced-high-contrast-colors/fast/css/forced-colors-mode/forced-colors-mode-15.html [ Pass Failure ]
+crbug.com/1167222 http/tests/websocket/multiple-connections-throttled.html [ Pass Failure ]