[FLINK-32495][connectors/common] Fix the bug that the shared thread factory causes the source alignment unit test to fail

[1996fanrui]

What is the purpose of the change

SourceCoordinatorAlignmentTest.testWatermarkAlignmentWithTwoGroups fails.

I analyzed this CI : https://dev.azure.com/apache-flink/apache-flink/_build/results?buildId=50668&view=logs&j=a57e0635-3fad-5b08-57c7-a4142d7d6fa9&t=2ef0effc-1da1-50e5-c2bd-aab434b1c5b7&l=9089

Root cause:

• The CoordinatorExecutorThreadFactory cannot new multiple threads. And too many callers will check coordinatorThreadFactory.isCurrentThreadCoordinatorThread(), such as: SourceCoordinatorContext.attemptReady.
• The CoordinatorExecutorThreadFactory is shared at SourceCoordinatorTestBase
• It will be used at multiple source coordinator, and the second source coordinator will overwrite the CoordinatorExecutorThreadFactory#t, so the check will fail for the first source.

Brief change log

Don't share the CoordinatorExecutorThreadFactory.

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): ( no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): ( no)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)

[flinkbot]

CI report:

• d35ae88 Azure: SUCCESS

Bot commands

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[RocMarshal]

Thank you @1996fanrui for the fix.
LGTM +1.

[1996fanrui]

Thanks to @RocMarshal for the quick review, merging.