[3.12] gh-132969: Fix exception/hang shutdown(wait=False) and a task exited abnormally #133220
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When shutdown is called with wait=False, the executor thread keeps running even after the ProcessPoolExecutor's state is reset. The executor then tries to replenish the worker processes pool resulting in an error and a potential hang when it comes across a worker that has died. Fixed the issue by having _adjust_process_count() return without doing anything if the ProcessPoolExecutor's state has been reset.
Added unit tests to validate two scenarios:
max_workers < num_tasks (exception)
max_workers > num_tasks (exception + hang)
ProcessPoolExecutor
raises exception or hangs the process whenshutdown(wait=False)
and worker throws exception #132969