Make FtpServer disposable about ftpserver HOT 3 OPEN

[Fact]
 public async Task Test()
        {
            // arrange
            var endPoint = new IPEndPoint(IPAddress.Loopback, 21);
            var ftpServer = new FtpServer(endPoint, Directory.GetCurrentDirectory());
            var cancellationTokenSource = new CancellationTokenSource();
            await ftpServer.RunAsync(cancellationTokenSource.Token);
            var ftpServerCaller = new FtpServerCaller();
            // act
            try
            {
                await ftpServerCaller.CallFtpServer();
            }
            finally
            {
                cancellationTokenSource.Cancel();
            }
            // assert
            ftpServerCaller.CheckResult();
        }

 [Fact]
        public async Task Test()
        {
            // arrange
            var endPoint = new IPEndPoint(IPAddress.Loopback, 21);
            using var ftpServer = new FtpServer(endPoint, Directory.GetCurrentDirectory());
            await ftpServer.RunAsync();
            var ftpServerCaller = new FtpServerCaller();
            // act
            await ftpServerCaller.CallFtpServer();
            // assert
            ftpServerCaller.CheckResult();
        }