Build: add dependabot workflow to update actions

Author: timmywil

Diff for: .github/dependabot.yml

@@ -0,0 +1,13 @@
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    directory: "/"
+    schedule:
+      interval: monthly
+
+    # Group all dependabot version update PRs into one
+    groups:
+      github-actions:
+        applies-to: version-updates
+        patterns:
+          - "*"