Fix feed used for darc init in shell scripts (#15822)

Author: mmitche

eng/common/darc-init.sh

@@ -68,7 +68,7 @@ function InstallDarcCli {
     fi
   fi
 
-  local arcadeServicesSource="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-tools/nuget/v3/index.json"
+  local arcadeServicesSource="https://pkgs.dev.azure.com/dnceng/public/_packaging/dotnet-eng/nuget/v3/index.json"
 
   echo "Installing Darc CLI version $darcVersion..."
   echo "You may need to restart your command shell if this is the first dotnet tool you have installed."