Meta: Add dependabot configuration to update github actions

Author: https://github.com/bgianfo
Commit: 87b18f9304
Pull-request: https://github.com/SerenityOS/serenity/pull/17040

.github/dependabot.yml

@@ -0,0 +1,11 @@
+# Set update schedule for GitHub Actions
+version: 2
+
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      # Check for updates to GitHub Actions every week
+      interval: "weekly"
+    commit-message:
+      prefix: "CI:"