chore: Update NuGet config to include nuget.org fallback

Co-authored-by: pmaytak <[email protected]>

Author: Copilot

NuGet.config

@@ -2,6 +2,6 @@
 <configuration>
   <packageSources>
     <clear />
-    <add key="dotnet-public" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-public/nuget/v3/index.json" />
+    <add key="nuget.org" value="https://api.nuget.org/v3/index.json" />
   </packageSources>
 </configuration>