Python3.12: Fix AttributeError

[penguinpee]

getattr(importlib.abc, "MetaPathFinder", importlib.abc.Finder)
throws AttributeError in Python3.12.

[penguinpee]

Tests were failing when running with Python3.12:

==================================== ERRORS ====================================
_______________ ERROR collecting pynetdicom/tests/test_assoc.py ________________
pynetdicom/tests/test_assoc.py:69: in <module>
    from .hide_modules import hide_modules
pynetdicom/tests/hide_modules.py:33: in <module>
    _ModuleHiderBase = getattr(importlib.abc, "MetaPathFinder", importlib.abc.Finder)
/usr/lib64/python3.12/importlib/abc.py:38: in __getattr__
    raise AttributeError(f'module {__name__!r} has no attribute {name!r}')
E   AttributeError: module 'importlib.abc' has no attribute 'Finder'
_____________ ERROR collecting pynetdicom/tests/test_transport.py ______________
pynetdicom/tests/test_transport.py:34: in <module>
    from .hide_modules import hide_modules
pynetdicom/tests/hide_modules.py:33: in <module>
    _ModuleHiderBase = getattr(importlib.abc, "MetaPathFinder", importlib.abc.Finder)
/usr/lib64/python3.12/importlib/abc.py:38: in __getattr__
    raise AttributeError(f'module {__name__!r} has no attribute {name!r}')
E   AttributeError: module 'importlib.abc' has no attribute 'Finder'

[mrbean-bremen]

Duplicate of #852?