Fix test flake

Fix the followin flake:
```
[ERROR] com.rabbitmq.mqtt.test.MqttTest.sessionRedelivery(TestInfo) -- Time elapsed: 0.959 s <<< FAILURE!
org.opentest4j.AssertionFailedError:
Expecting value to be false but was true
        at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at com.rabbitmq.mqtt.test.MqttTest.sessionRedelivery(MqttTest.java:523)
        at java.base/java.lang.reflect.Method.invoke(Method.java:566)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1541)
[ERROR] Failures:
[ERROR]   MqttTest.sessionRedelivery:523
Expecting value to be false but was true
```

Author: ansd

deps/rabbitmq_mqtt/test/java_SUITE_data/src/test/java/com/rabbitmq/mqtt/test/MqttTest.java

@@ -520,6 +520,7 @@ public void sessionRedelivery(TestInfo info) throws MqttException, InterruptedEx
     // Message has been delivered but connection has failed.
     waitAtMost(() -> receivedMessagesSize() == 1);
     assertThat(firstMessage().getPayload()).isEqualTo(payload);
+    Thread.sleep(100);
     assertThat(client.isConnected()).isFalse();
 
     receivedMessages.clear();