TestConnectWithFallback: increase timeout

on Windows connecting on a closed port takes about 2 seconds.
You can test with something like this

        start := time.Now()
	_, err := d.DialContext(context.Background(), "tcp", "127.0.0.1:1")
	fmt.Printf("finished, time %s, err: %v\n", time.Since(start), err)

This seems by design

https://groups.google.com/g/comp.os.ms-windows.programmer.win32/c/jV6kRVY3BqM

Generally TestConnectWithFallback takes about 8-9 seconds on Windows.
Increase timeout to avoid random failures under load

pgconn/pgconn_test.go

@@ -496,7 +496,7 @@ func TestConnectWithRuntimeParams(t *testing.T) {
 func TestConnectWithFallback(t *testing.T) {
 	t.Parallel()
 
-	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
 	defer cancel()
 
 	config, err := pgconn.ParseConfig(os.Getenv("PGX_TEST_DATABASE"))