update dependabot config

Author: woylie

.github/dependabot.yml

@@ -3,15 +3,13 @@ updates:
   - package-ecosystem: mix
     directory: "/"
     schedule:
-      interval: weekly
-      day: saturday
+      interval: monthly
   - package-ecosystem: mix
     directory: "/example"
     schedule:
-      interval: weekly
+      interval: monthly
       day: saturday
   - package-ecosystem: github-actions
     directory: "/"
     schedule:
-      interval: weekly
-      day: saturday
+      interval: monthly