Intermittent failure from test_traits_process_executor.TestTraitsExecutor.test_shutdown_timeout

[mdickinson]

I've seen the following failure locally a couple of times (usually while there are other CPU-intensive processes running on the machine), and once on CI. I'm fairly sure that this does not represent an issue with the business logic, but we may need to tweak the test. At a guess it's the rest of the process shutdown (e.g., the manager shutdown and the process pool shutdown) that's actually taking most of the time here.

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FAIL: test_shutdown_timeout (traits_futures.tests.test_traits_process_executor.TestTraitsExecutor)
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Traceback (most recent call last):
  File "/Users/mdickinson/Enthought/Projects/traits-futures/traits_futures/tests/traits_executor_tests.py", line 242, in test_shutdown_timeout
    self.assertLess(actual_timeout, 1.0)
AssertionError: 1.1583175519999998 not less than 1.0