test(qa): wait until message is published before restarting the broker

The test was flaky - it sometime failed in 'correlate message after restart' while waiting for the instance to be completed. It is not clear why exactly the test fails, but a probable reason is that the message was not published before the broker was restarted.

(cherry picked from commit fcef5b6)

qa/integration-tests/src/test/java/io/camunda/zeebe/it/clustering/CompleteProcessInstanceAfterLeaderChangeTest.java

@@ -76,7 +76,8 @@ public static Object[][] actions() {
                     .newPublishMessageCommand()
                     .messageName("msg")
                     .correlationKey("123")
-                    .send(),
+                    .send()
+                    .join(),
         (BiConsumer<ClusteringRule, GrpcClientRule>)
             (clusteringRule, clientRule) -> {
               final var processDefinitionKey =