🤖 Add dependabot for GHA get/stay current

Author: mtboren

.github/dependabot.yaml

@@ -0,0 +1,9 @@
+# Set update schedule for GitHub Actions; ref at https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    # Workflow files stored in the default location of `.github/workflows`. (You don't need to specify `/.github/workflows` for `directory`. You can use `directory: "/"`.)
+    directory: /
+    schedule:
+      # Check for updates to GitHub Actions every week
+      interval: weekly