Build/Test Tools: Configure Dependabot scanning for GitHub Actions.

This eliminates the need to manually check all GitHub Actions used within workflow files for updates.

Fixes #54503.

git-svn-id: https://develop.svn.wordpress.org/trunk@52241 602fd350-edb4-49c9-b593-d223f7449a82

.github/dependabot.yml

@@ -0,0 +1,9 @@
+# Configure Dependabot scanning.
+version: 2
+
+updates:
+  # Check for updates to GitHub Actions.
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"