chore: turn on dependabot monthly updates (#317)

* turn on dependabot montly updates

* No extraneous comment

---------

Co-authored-by: Nicholas Smith <nick.smith@cern.ch>

Author: lgray

.github/dependabot.yml

@@ -4,8 +4,6 @@ updates:
   - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
-      interval: "daily"
-    ignore:
-      # Official actions have moving tags like v1
-      # that are used, so they don't need updates here
-      - dependency-name: "actions/*"
+      interval: "monthly"
+    commit-message:
+      prefix: "ci: "