[sheriff] Mark no-hover-during-scroll.html flaky

Mark fast/scrolling/no-hover-during-scroll.html as flaky on all
platforms. Previously it was marked as flaky only on linux.

TBR=lanwei@chromium.org

Bug: 914782

No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I2f2333eb21c4f47453718fab706d71a3ba56aeb0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2225501Reviewed-by: Nina Satragno <nsatragno@chromium.org>
Commit-Queue: Nina Satragno <nsatragno@chromium.org>
Cr-Commit-Position: refs/heads/master@{#773789}

third_party/blink/web_tests/TestExpectations

@@ -4736,7 +4736,9 @@ crbug.com/913173 fast/backgrounds/background-svg-scaling-zoom.html [ Failure Pas
 
 # Sheriff 2018-12-13
 crbug.com/910452 media/controls/buttons-after-reset.html [ Pass Failure ]
-crbug.com/914782 [ Linux ] fast/scrolling/no-hover-during-scroll.html [ Pass Failure ]
+
+# Update 2020-06-01: flaky on all platforms.
+crbug.com/914782 fast/scrolling/no-hover-during-scroll.html [ Pass Failure ]
 
 # Sheriff 2018-12-14
 crbug.com/913931 [ Mac10.11 ] external/wpt/css/css-layout-api/auto-block-size-absolute.https.html [ Pass Failure ]