message: Fix race condition in test server
diff: @@ -558,6 +558,10 @@ fn test_pub_sub_2_clients() {
  let conn2 = nats::connect(&server.address().to_string()).unwrap();
  let sub = conn1.subscribe("*").unwrap();
  + // This test was sometimes failing due to some issues in `nats_test_server`.
  + // As it is neither recommended nor actively developed way to test features,
  + // sleep was added to circumvent the problem.
  + thread::sleep(Duration::from_millis(100));
  conn2.publish("subject", "message").unwrap();
  sub.next_timeout(Duration::from_millis(100)).unwrap();
  