Add expectation for wpt/html/COEP/reporting-to-endpoint.https.html

https://github.com/web-platform-tests/wpt/pull/25177 modified
wpt/html/COEP/reporting-to-endpoint.https.html, and that blocks
the WPT autoroller because the output depends on onetime tokens.
See https://chromium-review.googlesource.com/c/chromium/src/+/2371035
for example.

Add a failure expectation to unblock the autoroller.

Bug: 1119676
Change-Id: I99e17bee60d73ce6d2645693e8e48406092deb49
No-Try: True
Tbr: foolip@google.com
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2370685
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Cr-Commit-Position: refs/heads/master@{#800914}

third_party/blink/web_tests/TestExpectations

@@ -6710,3 +6710,5 @@ crbug.com/1120330 virtual/threaded/external/wpt/feature-policy/experimental-feat
 
 # Sheriff 2020-08-24
 crbug.com/1121015 [ Linux ] external/wpt/webcodecs/video-decoder.html [ Pass Crash ]
+
+crbug.com/1119676 external/wpt/html/cross-origin-embedder-policy/reporting-to-endpoint.https.html [ Failure ]
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