CSHARP-5661: Fix UnobservedTaskException on socket connecting timeout (#1742)

Author: sanych-sun

src/MongoDB.Driver/Core/Connections/TcpStreamFactory.cs

@@ -164,7 +164,11 @@ private async Task ConnectAsync(Socket socket, EndPoint endPoint, CancellationTo
 
             if (!connectTask.IsCompleted)
             {
-                try { socket.Dispose(); } catch { }
+                try
+                {
+                    connectTask.IgnoreExceptions();
+                    socket.Dispose();
+                } catch { }
 
                 cancellationToken.ThrowIfCancellationRequested();
                 throw new TimeoutException($"Timed out connecting to {endPoint}. Timeout was {_settings.ConnectTimeout}.");

tests/MongoDB.Driver.Tests/Core/Connections/TcpStreamFactoryTests.cs

@@ -185,6 +185,43 @@ public void CreateStream_should_connect_to_a_running_server_and_return_a_non_nul
             stream.Should().NotBeNull();
         }
 
+        [Fact]
+        public async Task CreateStream_should_not_produce_unobserved_exceptions_on_timeout()
+        {
+            // The purpose of this test is to attempt a connection that will reliably be rejected and throw exception the connection.
+            // By specifying a very short timeout, we expect a TimeoutException to occur before the connection exception.
+            // This test ensures that the connection exception is observed.
+            var subject = new TcpStreamFactory(new TcpStreamSettings(connectTimeout: TimeSpan.FromMilliseconds(1)));
+            var endpoint = new IPEndPoint(IPAddress.Parse("1.1.1.1"), 23456);
+
+            GC.Collect();
+            GC.WaitForPendingFinalizers();
+            var unobservedTaskExceptionRaised = false;
+
+            EventHandler<UnobservedTaskExceptionEventArgs> eventHandler = (s, args) =>
+            {
+                unobservedTaskExceptionRaised = true;
+            };
+
+            TaskScheduler.UnobservedTaskException += eventHandler;
+
+            try
+            {
+                var exception = await Record.ExceptionAsync(() => subject.CreateStreamAsync(endpoint, CancellationToken.None));
+                exception.Should().BeOfType<TimeoutException>();
+
+                Thread.Sleep(100);
+                GC.Collect();
+                GC.WaitForPendingFinalizers();
+            }
+            finally
+            {
+                TaskScheduler.UnobservedTaskException -= eventHandler;
+            }
+
+            unobservedTaskExceptionRaised.Should().BeFalse();
+        }
+
         [Theory]
         [ParameterAttributeData]
         public void SocketConfigurator_can_be_used_to_set_keepAlive(