WatchTest.testMultiplePollsWithManyResults flake: Outputs must be in timestamp order (sickbayed)

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• [Jenkins Job|https://builds.apache.org/job/beam_PreCommit_Java_Phrase/1258/testReport/junit/org.apache.beam.sdk.transforms/WatchTest/testMultiplePollsWithManyResults/]

Initial investigation:

java.lang.AssertionError: Drop timestamped input/Values/Map/ParMultiDo(Anonymous).output: Outputs must be in timestamp order

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