Handle tzinfo=None in arrow.get()

[ReinerBRO]

Fixes #1259.

When tzinfo=None is passed explicitly, ArrowFactory.get() now treats it the same as omitting tzinfo instead of incorrectly routing the call into the 3+ argument constructor path.

Validation:

• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 PYTHONPATH=. python -m pytest -c /dev/null tests/test_factory.py -k "kwarg_tzinfo_none or kwarg_tzinfo_string or no_args or insufficient_kwargs" -q
• PYTEST_DISABLE_PLUGIN_AUTOLOAD=1 PYTHONPATH=. python -m pytest -c /dev/null tests/test_factory.py -q
• ruff check arrow/factory.py tests/test_factory.py

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (b423717) to head (e306a27).

Additional details and impacted files

@@            Coverage Diff            @@
##            master     #1265   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines         2315      2316    +1     
  Branches       358       358           
=========================================
+ Hits          2315      2316    +1     

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