downstream test from sdk-platform-java for pubsublite multiple tests flaky

[zhumin8]

full log here

Error:  Errors: 
Error:    AckSetTrackerImplTest.trackAndAggregateAcks:94 » NullPointer Cannot invoke "com.google.api.core.ApiFuture.addListener(java.lang.Runnable, java.util.concurrent.Executor)" because "future" is null
Error:    SinglePartitionPublisherTest.publishResultTransformed:91 WrongTypeOfReturnValue 

another rerun log

Error:  Errors: 
Error:    SinglePartitionSubscriberTest.singleMessageNackHandlerFailedFuture:228 » IllegalState failureCause() is only valid if the service has failed, service is RUNNING

[zhumin8]

The last one is observed again:

Error:  Errors: 
Error:    SinglePartitionSubscriberTest.singleMessageNackHandlerFailedFuture:228 » IllegalState failureCause() is only valid if the service has failed, service is RUNNING

https://github.com/googleapis/java-pubsublite/actions/runs/16760822465/job/47621631421?pr=1906