Remove duplicate entry in Dependabot configuration and add github-actions ecosystem (#48)

ci(dependabot): Add `github-actions` ecosystem

Author: jamacku

.github/dependabot.yml

@@ -1,11 +1,14 @@
+# https://docs.github.com/en/github/administering-a-repository/keeping-your-actions-up-to-date-with-github-dependabot
+---
+
 version: 2
 updates:
   - package-ecosystem: "npm"
     directory: "/"
     schedule:
       interval: "daily"
-  # https://docs.github.com/en/github/administering-a-repository/keeping-your-actions-up-to-date-with-github-dependabot
-  - package-ecosystem: "npm"
+
+  - package-ecosystem: "github-actions"
     directory: "/"
     schedule:
-      interval: "daily"
+      interval: "monthly"