TImeout StreamingDataflowWorkerTest when test stuck

[Abacn]

mitigate #28957

A testing PR #23785 found a stuck test path

Class org.apache.beam.runners.dataflow.worker.StreamingDataflowWorkerTest

testActiveThreadMetric[0: [streamingEngine=false]]
org.junit.runners.model.TestTimedOutException: test timed out after 600 seconds
	at java.lang.Object.wait(Native Method)
	at java.lang.Object.wait(Object.java:502)
	at org.apache.beam.runners.dataflow.worker.StreamingDataflowWorkerTest.testActiveThreadMetric(StreamingDataflowWorkerTest.java:2850)
...

this would make the test under this test class timeout after 600s, instead the whole test suite hanging indefinitely

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[Abacn]

R: @ahmedabu98
CC: @kerrydc

[github-actions]

Stopping reviewer notifications for this pull request: review requested by someone other than the bot, ceding control

[Abacn]

e.g. this happened again in jenkins: https://ci-beam.apache.org/job/beam_PreCommit_Java_Commit/28702/

[Abacn]

Run Java PreCommit

[Abacn]

R: @edman124 @bvolpato

this test was recently added in #28513 . Besides adding a timeout, any chance to know why it could stuck indefinitely?

[edman124]

The notify could be called before we enter the synchronized block causing wait to wait indefinitely, this test should be fixed in #29041
LGTM as a temporary stopgap