Add PullRequests package source to nuget.config

Author: Arlodotexe

.github/workflows/config/nuget.config

@@ -2,6 +2,7 @@
   <packageSources>
     <clear />
     <add key="nuget.org" value="https://api.nuget.org/v3/index.json" protocolVersion="3" />
+    <add key="PullRequests" value="https://pkgs.dev.azure.com/dotnet/CommunityToolkit/_packaging/CommunityToolkit-PullRequests/nuget/v3/index.json" protocolVersion="3" />
     <add key="MainLatest" value="https://pkgs.dev.azure.com/dotnet/CommunityToolkit/_packaging/CommunityToolkit-MainLatest/nuget/v3/index.json" protocolVersion="3" />
   </packageSources>
   <disabledPackageSources>