KAFKA-8861 Fix flaky RegexSourceIntegrationTest.testMultipleConsumersCanReadFromPartitionedTopic (apache#7281)

similar to https://issues.apache.org/jira/browse/KAFKA-8011 and https://issues.apache.org/jira/browse/KAFKA-8026

Reviewers:  Matthias J. Sax <[email protected]>,  Bill Bejeck <[email protected]>

Author: chia7712

streams/src/test/java/org/apache/kafka/streams/integration/RegexSourceIntegrationTest.java

@@ -337,8 +337,8 @@ public void testMultipleConsumersCanReadFromPartitionedTopic() throws Exception
             partitionedStreamLeader.to(DEFAULT_OUTPUT_TOPIC, Produced.with(stringSerde, stringSerde));
             partitionedStreamFollower.to(DEFAULT_OUTPUT_TOPIC, Produced.with(stringSerde, stringSerde));
 
-            final List<String> leaderAssignment = new ArrayList<>();
-            final List<String> followerAssignment = new ArrayList<>();
+            final List<String> leaderAssignment = new CopyOnWriteArrayList<>();
+            final List<String> followerAssignment = new CopyOnWriteArrayList<>();
 
             partitionedStreamsLeader  = new KafkaStreams(builderLeader.build(), streamsConfiguration, new DefaultKafkaClientSupplier() {
                 @Override