chore: preserve MessageDataMatcher from being deleted by owl bot

Author: mpeddada1

.github/.OwlBot.yaml

@@ -34,6 +34,7 @@ deep-preserve-regex:
 - "/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/FakePublisherServiceImpl.java"
 - "/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/FakeScheduledExecutorService.java"
 - "/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/FakeSubscriberServiceImpl.java"
+- "/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/MessageDataMatcher.java"
 - "/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/MessageDispatcherTest.java"
 - "/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/OpenCensusUtilTest.java"
 - "/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/v1/PublisherImplTest.java"