add Dispose in DisposeAsyncCore

Emby.Server.Implementations/HttpServer/WebSocketConnection.cs

@@ -276,6 +276,7 @@ namespace Emby.Server.Implementations.HttpServer
             if (_socket.State == WebSocketState.Open)
             {
                 await _socket.CloseOutputAsync(WebSocketCloseStatus.NormalClosure, "System Shutdown", CancellationToken.None).ConfigureAwait(false);
+                _socket.Dispose();
             }
         }
     }