fix: nuget building flake (#1039)

Author: bitsandfoxes

NuGet.config

@@ -3,6 +3,6 @@
   <packageSources>
     <!--To inherit the global NuGet package sources remove the <clear/> line below -->
     <clear />
-    <add key="nuget" value="https://api.nuget.org/v3/index.json" />
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
   </packageSources>
 </configuration>