gh-92886: Fix tests that fail when running with optimizations (-O) in _test_multiprocessing.py

[jackh-ncl]

#92886

Before:

$ ./python.exe -Om unittest test._test_multiprocessing
...........s.............s........F..F................
======================================================================
FAIL: test_dict (test._test_multiprocessing.TestSyncManagerTypes.test_dict)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/Users/.../dev/cpython/Lib/test/_test_multiprocessing.py", line 5726, in test_dict
self.assertEqual(len(o), 0)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 1 != 0
======================================================================
FAIL: test_list (test._test_multiprocessing.TestSyncManagerTypes.test_list)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/Users/.../dev/cpython/Lib/test/_test_multiprocessing.py", line 5708, in test_list
self.assertEqual(len(o), 0)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError: 1 != 0
----------------------------------------------------------------------
Ran 54 tests in 24.460s
FAILED (failures=2, skipped=2)

After:

$ ./python.exe -Om unittest test._test_multiprocessing
...........s.............s............................
----------------------------------------------------------------------
Ran 54 tests in 24.588s
OK (skipped=2)

[bedevere-bot]

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[jackh-ncl]

Could be worth changing the rest of the assertions in this file?

[iritkatriel]

Thanks.