[PreCommit_Java] [Flake] UnboundedSourceWrapperTest$ParameterizedUnboundedSourceWrapperTest

Test:

org.apache.beam.runners.flink.translation.wrappers.streaming.io.UnboundedSourceWrapperTest$ParameterizedUnboundedSourceWrapperTest >> testWatermarkEmission[numTasks = 1; numSplits=1]

Fails with the following exception:

org.junit.runners.model.TestTimedOutException: test timed out after 30000 milliseconds

Affected Jenkins job: https://builds.apache.org/job/beam_PreCommit_Java_Phrase/1665/

Gradle build scan: https://scans.gradle.com/s/nvgeb425fe63q