authorizenet lib is incompatible with setuptools >=78

[jusdino]

Python versions using the latest version of setuptools (currently 78.0.1) cannot install this library:

setup.cfg is using a long-deprecated argument that just needs updating.

See this PR for the fix.

[jusdino]

Just FYI - the fix may be slightly more complex, but still not a big issue, if we can just get some attention from the maintainers:
#165 (comment)