[NuGet.Config] Add temporary feed to find some newer .NET 6 packs.

NuGet.config

@@ -24,6 +24,10 @@
     <add key="macios-dependencies" value="https://pkgs.dev.azure.com/xamarin/public/_packaging/macios-dependencies/nuget/v3/index.json" />
     <add key="xamarin-impl" value="https://pkgs.dev.azure.com/azure-public/vside/_packaging/xamarin-impl/nuget/v3/index.json" />
     <add key="local-tests-feed" value="tests/.nuget/packages" />
+
+    <!-- These feeds are from main (6.0.4xx runtime branch) to get 6.0.9 versions of numerous .NET 6 packages. It should be possible to remove this after a while. -->
+    <add key="darc-pub-dotnet-emsdk-3f6c45a" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/darc-pub-dotnet-emsdk-3f6c45a2/nuget/v3/index.json" />
+    <add key="darc-pub-dotnet-runtime-531f715" value="https://pkgs.dev.azure.com/dnceng/public/_packaging/darc-pub-dotnet-runtime-531f715f/nuget/v3/index.json" />
   </packageSources>
   <disabledPackageSources>
     <clear />