fix pythonCollectionFromPropertyList fails on converting dates prior to year 1970

[ZigZagT]

Fixes a issue where pythonCollectionFromPropertyList crashes on dates prior to year 1970.

Both NSDate and python's datetime classes are capable of handling dates prior to 1970/01/01. However, the datetime.fromtimestamp API does not. It would throw the following exception:

  File "/opt/homebrew/lib/python3.11/site-packages/PyObjCTools/Conversion.py", line 220, in pythonCollectionFromPropertyList
    return datetime.datetime.fromtimestamp(aCollection.timeIntervalSince1970())
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
ValueError: year 0 is out of range

[ZigZagT]

pre-commit is not working

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(timeout after 180 seconds)