message: style: fix warning in examples
  This fixes a new compiler warning in the `tower-load` example.
diff: @@ -318,8 +318,8 @@ async fn load_gen(addr: SocketAddr) -> Result<(), Err> {
  .layer(request_span::layer(req_span))
  .timeout(Duration::from_millis(200))
  .service(Client::new());
  -
  - while let Some(_) = time::interval(Duration::from_millis(50)).next().await {
  + let mut interval = time::interval(Duration::from_millis(50));
  + while interval.next().await.is_some() {
  let authority = format!("{}", addr);
  let mut svc = svc.clone().ready_oneshot().await?;
  