Use dependabot to periodically check for updated actions.

Author: mmuetzel

.github/dependabot.yml

@@ -0,0 +1,8 @@
+version: 2
+updates:
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      # Check for updates to GitHub Actions every week
+      interval: "weekly"