Update ci-testing.yml (ultralytics#4770)

Author: glenn-jocher

.github/workflows/ci-testing.yml

@@ -8,6 +8,8 @@ on: # https://help.github.com/en/actions/reference/events-that-trigger-workflows
   pull_request:
     # The branches below must be a subset of the branches above
     branches: [master, develop]
+  schedule:
+    - cron: '0 0 * * *'  # Runs at 00:00 UTC every day
 
 jobs:
   cpu-tests: