Update services.md (#22650)

aspnetcore/grpc/services.md

@@ -73,7 +73,7 @@ public class GreeterService : GreeterBase
 {
     public override Task<HelloReply> SayHello(HelloRequest request, ServerCallContext context)
     {
-        return Task.FromResult(new HelloRequest { Message = $"Hello {request.Name}" });
+        return Task.FromResult(new HelloReply { Message = $"Hello {request.Name}" });
     }
 }
 ```