Update dependabot.yml

Author: Harmanpreet-Microsoft

.github/dependabot.yml

@@ -22,3 +22,12 @@ updates:
       prefix: "build"
     target-branch: "dependabotchanges"
     open-pull-requests-limit: 100
+    
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "monthly"
+    commit-message:
+      prefix: "build"
+    target-branch: "dependabotchanges"
+    open-pull-requests-limit: 100