message: Fix Mutex usage in asynk::client::cleanup_subscriptions function.
diff: @@ -557,7 +557,10 @@ impl Client {
  /// Sends UNSUB for dead subscriptions.
  async fn cleanup_subscriptions(&self, state: &mut async_mutex::MutexGuard<'_, State>) {
  - for sid in mem::replace(&mut *self.unsubscribed.lock().unwrap(), HashSet::new()) {
  + // Keep unsubscribed list in separate variable so it won't be captured by for loop context.
  + let unsubscribed = mem::replace(&mut *self.unsubscribed.lock().unwrap(), HashSet::new());
  +
  + for sid in unsubscribed {
  // Remove the subscription from the map.
  state.subscriptions.remove(&sid);
  