gRPC Channel is disposed of after use (#16432)

Author: arialdomartini

aspnetcore/tutorials/grpc/grpc-start/sample/GrpcGreeterClient/Program.cs

@@ -13,7 +13,7 @@ class Program
         static async Task Main(string[] args)
         {
             // The port number(5001) must match the port of the gRPC server.
-            var channel = GrpcChannel.ForAddress("https://localhost:5001");
+            using var channel = GrpcChannel.ForAddress("https://localhost:5001");
             var client =  new Greeter.GreeterClient(channel);
             var reply = await client.SayHelloAsync(
                               new HelloRequest { Name = "GreeterClient" });