Use dependabot for Nuget instead of NPM

Author: wtgodbe

.github/dependabot.yml

@@ -6,15 +6,13 @@ registries:
     url: https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public-npm/npm/registry/
 
 updates:
-  - package-ecosystem: npm
+  - package-ecosystem: NuGet
     directory: "/"
     # Perform only security updates of our npm dependencies.
     open-pull-requests-limit: 0
-    registries:
-    - dev.azure.com
     # Schedule should be ignored for security updates.
     schedule:
-      interval: monthly
+      interval: weekly
 
   - package-ecosystem: "github-actions"
     directory: "/"