Attempt to eliminate test flake

This commit attempts to eliminate the test flake described in
#12413 (comment)

```
rabbitmq_mqtt > parallel-ct-set-1 > mqtt_shared_SUITE > cluster_size_3 > v4 rabbit_mqtt_qos0_queue_kill_node

=== Ended at 2024-10-01 09:59:52
=== Location: [{mqtt_shared_SUITE,rabbit_mqtt_qos0_queue_kill_node,[1165](https://github.com/rabbitmq/rabbitmq-server/issues/mqtt_shared_suite.src.html#1165)},
              {test_server,ts_tc,1793},
              {test_server,run_test_case_eval1,1302},
              {test_server,run_test_case_eval,1234}]
=== === Reason: no match of right hand side value {publish_not_received,
                                                    <<"m1">>}
  in function  mqtt_shared_SUITE:rabbit_mqtt_qos0_queue_kill_node/1 (mqtt_shared_SUITE.erl, line 1165)
  in call from test_server:ts_tc/3 (test_server.erl, line 1793)
  in call from test_server:run_test_case_eval1/6 (test_server.erl, line 1302)
  in call from test_server:run_test_case_eval/9 (test_server.erl, line 1234)
```

This flake could not be reproduced locally.
This commit also assumes that this flake occurred under Khepri but not
under Mnesia.

The hypothesis is the following:
* Node 0 is down
* MQTT client creates binding on node 1
* Khepri commits since the binding is replicated and persisted on node 1
  and node 2. However the binding isn't reflected yet in node 2's
  routing projecting table.
* Publishing a message to node 2 routes to nowhere.

(cherry picked from commit 17df1b9)

deps/rabbitmq_mqtt/test/shared_SUITE.erl

@@ -1145,6 +1145,7 @@ rabbit_mqtt_qos0_queue_kill_node(Config) ->
     %% Re-connect to a live node with same MQTT client ID.
     Sub1 = connect(SubscriberId, Config, 1, []),
     {ok, _, [0]} = emqtt:subscribe(Sub1, Topic2, qos0),
+    ok = await_metadata_store_consistent(Config, 2),
     ok = emqtt:publish(Pub, Topic2, <<"m1">>, qos0),
     ok = expect_publishes(Sub1, Topic2, [<<"m1">>]),
     %% Since we started a new clean session, previous subscription should have been deleted.