CI: Add Dependabot to keep GitHub Actions updated

.github/dependabot.yml

@@ -0,0 +1,15 @@
+# Keep GitHub Actions up to date with GitHub's Dependabot
+# https://docs.github.com/en/code-security/dependabot/working-with-dependabot/keeping-your-actions-up-to-date-with-dependabot
+# https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#package-ecosystem
+
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    groups:
+      github-actions:
+        patterns:
+          - "*"  # Group all Actions updates into a single larger pull request    
+    schedule:
+      # Check for updates to GitHub Actions every week
+      interval: "weekly"