Disable supported-stats to fix webrtc roll

New stats added in https://webrtc-review.googlesource.com/c/src/+/208960
and https://webrtc-review.googlesource.com/c/src/+/209000 break this test.
Temorarily disable to unblock the roll and fix the expectations once
merged.

Bug: webrtc:11429
Change-Id: Ifbd68a27069e2e79425500747205a586b8894ea1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2727506
Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Evan Shrubsole <eshr@google.com>
Cr-Commit-Position: refs/heads/master@{#859019}

third_party/blink/web_tests/TestExpectations

@@ -5740,5 +5740,8 @@ crbug.com/614958 virtual/webrtc-wpt-plan-b/external/wpt/webrtc/RTCPeerConnection
 # Sheriff 2021-03-01
 crbug.com/1183243 [ Linux ] http/tests/devtools/console/console-external-array.js [ Pass Failure ]
 
+# Webrtc-in-Chrome 2021-03-01
+crbug.com/webrtc/12507 external/wpt/webrtc-stats/supported-stats.html [ Pass Failure ]
+
 # Temporarily disabled for https://crrev.com/c/2713104
 crbug.com/v8/11429 http/tests/devtools/profiler/cpu-profiler-profiling.js [ Pass Failure ]