Updates the heartbeat for the given task IDs to prevent them from
        timing out and being requeued.

def _heartbeat(self, queue, task_ids):
        """
        Updates the heartbeat for the given task IDs to prevent them from
        timing out and being requeued.
        """
        now = time.time()
        self.connection.zadd(self._key(ACTIVE, queue),
                             **{task_id: now for task_id in task_ids})