Mark fast/forms/month/month-appearance-l10n.html as failing on Mac10.10

TBR=ftang@chromium.org

Bug: 1020034
Change-Id: If72015dc9ed501aebc92689d63b52856cbfdc8fb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1890397Reviewed-by: Alice Boxhall <aboxhall@chromium.org>
Commit-Queue: Alice Boxhall <aboxhall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711126}

third_party/blink/web_tests/TestExpectations

@@ -5770,3 +5770,6 @@ crbug.com/940927 external/wpt/trusted-types/trusted-types-eval-reporting-report-
 crbug.com/940927 external/wpt/trusted-types/trusted-types-eval-reporting.tentative.https.html [ Failure ]
 crbug.com/940927 external/wpt/trusted-types/trusted-types-eval-reporting-no-unsafe-eval.tentative.https.html [ Timeout ]
 crbug.com/940927 external/wpt/trusted-types/eval-with-permissive-csp.tentative.html [ Failure ]
+
+# Sheriff 2019-10-31
+crbug.com/1020034 [ Mac10.10 ] fast/forms/month/month-appearance-l10n.html [ Failure ]
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