private void transitionToUnsubscribed() {
        transitionTo(MemberState.UNSUBSCRIBED);
        leaveGroupInProgress.get().complete(null);
        leaveGroupInProgress = Optional.empty();
    }
Transition out of the {@link MemberState#LEAVING} state even if the heartbeat was not sent.
This will ensure that the member is not blocked in {@link MemberState#LEAVING} (it's the best
effort to send the request, without any response handling or retry logic).
clients/src/main/java/org/apache/kafka/clients/consumer/internals/ShareMembershipManager.java