ci: Schedule tests once an hour (#2999)

Run tests once every hour to get some data on how long they take and
what the failure rate is.
We hypothesize that tests take longer and fail more often when the US is
online.

.github/workflows/test.yml

@@ -26,6 +26,14 @@ on:
       - 'Samples/iOS-Swift/iOS-Swift.xcodeproj/xcshareddata/xcschemes/iOS-Swift.xcscheme'
       - 'Samples/macOS-Swift/macOS-Swift.xcodeproj/xcshareddata/xcschemes/macOS-Swift.xcscheme'
       - 'Samples/iOS-ObjectiveC/iOS-ObjectiveC.xcodeproj/xcshareddata/xcschemes/iOS-ObjectiveC.xcscheme'
+
+  schedule:
+    # Run tests every hour to get some data on how long they take and how often they fail.
+    # We hypothesize that tests take longer and fail more often when the US is online.
+    # The plan is to remove this after a week or so, once we have enough data.
+    # We didn't choose 0 to minimize collisions with other workflows.
+    # Run every hour at 17 minutes past the hour.
+    - cron:  '47 * * * *'
 
 jobs:
   build-test-server: