sheriff: Update test expectations

Mark
compositing/layer-creation/overflow-scroll-overlap.html
as failing on Mac

This appears to have been broken by CL:2146093 which won't revert
cleanly at this point.

TBR=szager@chromium.org,wangxianzhu@chromium.org,pdr@chromium.org

Bug: 1069546
Change-Id: I8a72c5e9e4e9d61df0365f4bb6b4158a6a11b9d1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2359317Reviewed-by: Fergus Dall <sidereal@google.com>
Commit-Queue: Fergus Dall <sidereal@google.com>
Cr-Commit-Position: refs/heads/master@{#798522}

third_party/blink/web_tests/TestExpectations

@@ -6738,3 +6738,6 @@ crbug.com/1046784 http/tests/devtools/network/network-content-replacement-xhr.js
 
 # Sheriff 2020-08-14
 crbug.com/1116681 [ Mac ] fast/frames/iframe-scaling-with-scroll.html [ Pass Failure ]
+
+# Sheriff 2020-08-17
+crbug.com/1069546 [ Mac ] compositing/layer-creation/overflow-scroll-overlap.html [ Pass Failure ]
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