Fix issue #590: Behavior change in argparse._parse_optional breaks the parse of optional arguments

[eggry]

What does this PR do?

In Python 3.13 and 3.12.7, the behavior of _parse_optional has changed to return a list of tuples: python/cpython#124631
This change would break the argument parser of this library.
For example, the existing unit test failed, resulting in:

FAILED jsonargparse_tests/test_dataclass_like.py::test_optional_dataclass_single_param_change - argparse.ArgumentError: cannot unpack non-iterable ActionTypeHint object

This PR will detect this behavior and return the proper format accordingly.
This PR resolves issue #590.

Before submitting

• Did you read the contributing guideline?
• [n/a] Did you update the documentation? (readme and public docstrings)
• [n/a] Did you write unit tests such that there is 100% coverage on related code? (required for bug fixes and new features)
• Did you verify that new and existing tests pass locally?
• Did you make sure that all changes preserve backward compatibility?
• Did you update the CHANGELOG? (not for typos, docs, test updates, or minor internal changes/refactors)

[mauvilsa]

Thank you very much for the fix!

Please add at the top of the changelog an entry for this fix, in a new section, like:

v4.33.2 (2024-10-??)
--------------------

Fixed
^^^^^
- ...

Also, since this breaking change also affects argcomplete and we don't know when there will be a new release with the fix, please add to test_argcomplete.py the following:

@pytest.fixture(autouse=True)
def temporal_skip_if_py312():
    if sys.version_info[:2] == (3, 12):
        pytest.skip("currently failing on 3.12 due to argparse breaking change")

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (a8b8b15) to head (b706c1e).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #591   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           22        22           
  Lines         6451      6453    +2     
=========================================
+ Hits          6451      6453    +2     

Flag	Coverage Δ
py3.10	85.91% <50.00%> (-0.02%)	⬇️
py3.10_all	98.83% <50.00%> (-0.02%)	⬇️
py3.10_pydantic1	49.15% <50.00%> (+<0.01%)	⬆️
py3.10_pydantic2	48.93% <50.00%> (+<0.01%)	⬆️
py3.10_types	98.85% <50.00%> (-0.02%)	⬇️
py3.11	85.88% <0.00%> (-0.03%)	⬇️
py3.11_all	98.79% <0.00%> (-0.04%)	⬇️
py3.11_types	98.80% <0.00%> (-0.04%)	⬇️
py3.12	86.03% <100.00%> (-0.02%)	⬇️
py3.12_all	97.86% <100.00%> (-0.97%)	⬇️
py3.12_types	97.87% <100.00%> (-0.97%)	⬇️
py3.8	86.54% <50.00%> (-0.02%)	⬇️
py3.8_all	99.47% <50.00%> (-0.02%)	⬇️
py3.8_types	99.50% <50.00%> (-0.02%)	⬇️
py3.9	86.46% <50.00%> (-0.02%)	⬇️
py3.9_all	99.42% <50.00%> (-0.02%)	⬇️
py3.9_types	99.44% <50.00%> (-0.02%)	⬇️

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