update dependabot.yml to cover .github/actions/ for GHA updates

Author: emilykl

.github/dependabot.yml

@@ -20,7 +20,9 @@ updates:
 
   # Update pinned versions for third-party GitHub Actions workflows
   - package-ecosystem: "github-actions"
-    directory: "/"
+    directories:
+      - "/"                   # Only covers .github/workflows/
+      - "/.github/actions/*"  # Covers all subdirectories under .github/actions/
     schedule:
       interval: "weekly"
     groups: