[Sheriff] Update test expectations for scrollbars/custom-scrollbar-adjust-on-inactive-pseudo.html

The test has been flaky on Mac:
https://analysis.chromium.org/p/chromium/flake-portal/flakes/occurrences?key=ag9zfmZpbmRpdC1mb3ItbWVyXgsSBUZsYWtlIlNjaHJvbWl1bUBibGlua193ZWJfdGVzdHNAc2Nyb2xsYmFycy9jdXN0b20tc2Nyb2xsYmFyLWFkanVzdC1vbi1pbmFjdGl2ZS1wc2V1ZG8uaHRtbAw

TBR=tkent@chromium.org

Bug: 1105271
Change-Id: Ia94cbbb1cc84f27846bedc42f50b7b5c46c066ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2303091Reviewed-by: Sahel Sharify <sahel@chromium.org>
Commit-Queue: Sahel Sharify <sahel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789171}

third_party/blink/web_tests/TestExpectations

@@ -6869,6 +6869,7 @@ crbug.com/1104910 [ Linux ] external/wpt/referrer-policy/gen/worker-module.http-
 
 crbug.com/1105270 [ Mac10.15 ] fast/events/open-window-from-another-frame.html [ Pass Timeout ]
 crbug.com/1105271 [ Mac ] virtual/prefer_compositing_to_lcd_text/scrollbars/custom-scrollbar-adjust-on-inactive-pseudo.html [ Pass Failure ]
+crbug.com/1105271 [ Mac ] scrollbars/custom-scrollbar-adjust-on-inactive-pseudo.html [ Pass Failure ]
 crbug.com/1105274 http/tests/devtools/tracing/timeline-js/timeline-js-line-level-profile-no-url-end-to-end.js [ Pass Timeout Failure ]
 crbug.com/1105275 [ Mac ] fast/dom/Window/window-onFocus.html [ Pass Failure ]