[Release-2.73] Cherry-pick #38083 into release branch

[Abacn]

Ensure LazyFlinkSourceSplitEnumerator handle splits happens after initialized

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Summary of Changes

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This pull request addresses a potential race condition in the Flink runner's source split enumeration. By introducing explicit synchronization, it guarantees that the system will not attempt to process split requests before the necessary initialization steps are complete, thereby enhancing the stability and correctness of Flink-based pipelines.

Highlights

• Concurrency Control: Implemented a synchronization mechanism using CountDownLatch and a volatile flag in LazyFlinkSourceSplitEnumerator to ensure that split requests are handled only after splits have been fully initialized.
• CI Configuration Update: Updated the revision number in the beam_PostCommit_Java_Jpms_Flink_Java11.json CI trigger file.

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