Disable flaky sample-on-last-keyframe.html test

This test is flaky on Mac and Linux builders.
Example failure: https://ci.chromium.org/ui/p/chromium/builders/ci/mac12-arm64-rel-tests/1239/overview

Bug: 1348835
Change-Id: I1fe8b265f21750db3c1bc81a27bc5d01a14ff07a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3801925
Commit-Queue: Takashi Sakamoto <tasak@google.com>
Reviewed-by: Takashi Sakamoto <tasak@google.com>
Cr-Commit-Position: refs/heads/main@{#1030092}

third_party/blink/web_tests/TestExpectations

@@ -7087,3 +7087,7 @@ crbug.com/1348447 [ Linux ] external/wpt/IndexedDB/blob-composite-blob-reads.any
 crbug.com/1348447 [ Linux ] external/wpt/IndexedDB/blob-composite-blob-reads.any.html [ Failure Pass Timeout ]
 crbug.com/1348447 [ Linux ] virtual/third-party-storage-partitioning/external/wpt/IndexedDB/blob-composite-blob-reads.any.worker.html [ Failure Pass Timeout ]
 crbug.com/1347675 virtual/fenced-frame-mparch/wpt_internal/fenced_frame/fragment-navigation.https.html [ Pass Timeout ]
+
+# Sheriff 2022-08-01
+crbug.com/1348835 [ Linux ] virtual/threaded-no-composited-antialiasing/animations/sample-on-last-keyframe.html [ Failure Pass ]
+crbug.com/1348835 [ Mac ] virtual/threaded-no-composited-antialiasing/animations/sample-on-last-keyframe.html [ Failure Pass ]