ci: run saucelabs legacy tests every hour (#28903)

Initially when we introduced the cronjob for Saucelabs,
we specified that the tests should run every 4h. Since the
caretaker needs more recent results when merging PRs
or before creating a release, we should run the saucelabs
tests every hour. This still ensures that PRs are not
affected by Saucelabs flakiness or incidents, and
the caretaker can also react better to real browser
failures (and isn't blocked on a 4h time frame)

PR Close #28903

.circleci/config.yml

@@ -615,8 +615,12 @@ workflows:
       - legacy-unit-tests-saucelabs
     triggers:
       - schedule:
-          # Runs the Saucelabs legacy tests every four hours.
-          cron: "0 0,4,8,12,16,20 * * *"
+          # Runs the Saucelabs legacy tests every hour. We still want to run Saucelabs
+          # frequently as the caretaker needs up-to-date results when merging PRs or creating
+          # a new release. Also we primarily moved the Saucelabs job into a cronjob that doesn't
+          # run for PRs, in order to ensure that PRs are not affected by Saucelabs flakiness or
+          # incidents. This is still guaranteed (even if we run the job every hour).
+          cron: "0 * * * *"
           filters: *publish_branches_filter
 
   aio_monitoring: