run coverage workflow manually and scheduled

.github/workflows/test-coverage.yaml

@@ -1,12 +1,11 @@
 # Workflow derived from https://github.com/r-lib/actions/tree/v2/examples
 # Need help debugging build failures? Start at https://github.com/r-lib/actions#where-to-find-help
 on:
-  push:
-    branches: [main, master]
-  pull_request:
-    branches: [main, master]
+  workflow_dispatch:  # Allow manual triggers
+  schedule:
+    - cron: '0 8 * * 4'
 
-name: test-coverage.yaml
+name: Coverage testing
 
 permissions: read-all