[3.14] Fix multiprocessing queue test_get() (GH-142024) (#142070)

[3.14] Fix multiprocessing queue test_get() (GH-142024) (#142070)

Fix multiprocessing queue test_get() (GH-142024)

* Replace sleep() with support.sleeping_retry().
* Test get_nowait() first.
* Restore previously disabled test.

Fix the failure:

FAIL: test_get (test.test_multiprocessing_spawn.test_processes.WithProcessesTestQueue.test_get)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "Lib/test/_test_multiprocessing.py", line 1208, in test_get
    self.assertEqual(queue_empty(queue), False)
    ~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: True != False
(cherry picked from commit 5e749d3743621be4c8bf5618ed3249e9fde9a599)

Co-authored-by: Victor Stinner <vstinner@python.org>