Update dependabot.yml: reduce frequency, add gh actions

Author: Pfeil

.github/dependabot.yml

@@ -7,5 +7,9 @@ version: 2
 updates:
   - package-ecosystem: "npm" # See documentation for possible values
     directory: "/" # Location of package manifests
+    schedule:
+      interval: "monthly"
+  - package-ecosystem: "github-actions"
+    directory: "/"
     schedule:
       interval: "weekly"