Change package-ecosystem from '.net' to 'NuGet'

Author: vaclavhluzek

.github/dependabot.yml

@@ -5,7 +5,7 @@
 
 version: 2
 updates:
-  - package-ecosystem: ".net" # See documentation for possible values
+  - package-ecosystem: "NuGet" # See documentation for possible values
     directory: "/" # Location of package manifests
     schedule:
       interval: "weekly"