update dependabot config

This changes update frequency to monthly- will kelp keep things a bit quieter and the git history tidier.
Adds GitHub Actions updates.

Author: coliff

.github/dependabot.yml

@@ -3,7 +3,10 @@ updates:
   - package-ecosystem: npm
     directory: "/"
     schedule:
-      interval: weekly
-    open-pull-requests-limit: 10
+      interval: monthly
     versioning-strategy: increase
-    
+  - package-ecosystem: github-actions
+    directory: "/"
+    schedule:
+      interval: monthly
+