[benchmarking] Fix accidental enabling of ct test on Mac.

This change
https://chromium-review.googlesource.com/c/chromium/src/+/1908715
accidentally enabled this test on Mac.

R=ellyjones@chromium.org

Bug: 1023255, 1028240
Change-Id: I13817e90e01b1dc3ae7474ea16b3f29c33832c6e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1937142Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Caleb Rouleau <crouleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719286}

tools/perf/contrib/cluster_telemetry/screenshot_unittest.py

@@ -11,7 +11,10 @@ from contrib.cluster_telemetry import screenshot
 
 
 class ScreenshotUnitTest(legacy_page_test_case.LegacyPageTestCase):
-  @decorators.Disabled('linux')
+  # This test should only run on linux, but it got disabled on Linux as
+  # well because of crbug.com/1023255. Replace the following with
+  # @decorators.Enabled('linux') once this is fixed on linux.
+  @decorators.Disabled('all')
   def testScreenshot(self):
     # Screenshots for Cluster Telemetry purposes currently only supported on
     # Linux platform.