[FLINK-39914][runtime] Fix flaky TaskDeploymentDescriptorFactoryTest#testHybridVertexFinish caused by async TDD creation

[och5351]

What is the purpose of the change

Execution.deploy() now creates TaskDeploymentDescriptor asynchronously, which means the IO executor thread calls jobMasterMainThreadExecutor.execute() to hand off the work.

The problem is that forMainThread() captures the calling thread at the time of its creation and asserts inside execute() that only that same thread can call it.

Since the IO executor thread calls execute() instead, the assertion fires and throws an AssertionError. This error then bubbles up through the CompletableFuture chain, flipping the producer vertex into FAILED state, which causes an IllegalStateException when the consumer vertex tries to read from it.

Brief change log

Updated buildExecutionGraph() in TaskDeploymentDescriptorFactoryTest to replace forMainThread() with forSingleThreadExecutor() and add proper async handling to accommodate the asynchronous TaskDeploymentDescriptor creation in Execution.deploy().

Verifying this change

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

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / JavaDocs / not documented)

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[RocMarshal]

Thanks @och5351 LGTM +1.

[flinkbot]

CI report:

• 5d84c11 Azure: FAILURE

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