Unit test failure under Python 3.12

[Thomas Goirand]

Hi,

After solving many unit test failures (for which I'll send patches), there's still what's below when building under Debian Unstable (and therefore, Python 3.12). Please help me to solve that last one.

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FAIL: mistral.tests.unit.scheduler.test_default_scheduler.DefaultSchedulerTest.test_pickup_from_job_store
mistral.tests.unit.scheduler.test_default_scheduler.DefaultSchedulerTest.test_pickup_from_job_store
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testtools.testresult.real._StringException: Traceback (most recent call last):
  File "/usr/lib/python3.12/unittest/mock.py", line 1387, in patched
    return func(*newargs, **newkeywargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/<<PKGBUILDDIR>>/mistral/tests/unit/scheduler/test_default_scheduler.py", line 161, in test_pickup_from_job_store
    self._wait_target_method_end()
  File "/<<PKGBUILDDIR>>/mistral/tests/unit/scheduler/test_default_scheduler.py", line 83, in _wait_target_method_end
    self.target_mtd_finished.wait()
  File "/usr/lib/python3/dist-packages/eventlet/event.py", line 125, in wait
    result = hub.switch()
             ^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/eventlet/hubs/hub.py", line 313, in switch
    return self.greenlet.switch()
           ^^^^^^^^^^^^^^^^^^^^^^
eventlet.timeout.Timeout: 15 seconds