Fix Callable type with subclass return not showing the --*.help option.

[mauvilsa]

What does this PR do?

Fixes #566

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• [n/a] Did you update the documentation? (readme and public docstrings)
• 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)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (e5ff8bc) to head (cc954fd).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #567   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           22        22           
  Lines         6445      6441    -4     
=========================================
- Hits          6445      6441    -4     

Flag	Coverage Δ
py3.10	85.72% <98.30%> (-0.01%)	⬇️
py3.10_all	98.69% <100.00%> (-0.01%)	⬇️
py3.10_pydantic1	48.74% <59.32%> (+0.01%)	⬆️
py3.10_pydantic2	48.53% <59.32%> (+0.01%)	⬆️
py3.10_types	98.71% <100.00%> (-0.01%)	⬇️
py3.11	85.68% <98.30%> (-0.04%)	⬇️
py3.11_all	98.66% <100.00%> (-0.04%)	⬇️
py3.11_types	98.67% <100.00%> (-0.04%)	⬇️
py3.12	85.82% <98.30%> (-0.04%)	⬇️
py3.12_all	98.66% <100.00%> (-0.04%)	⬇️
py3.12_types	98.67% <100.00%> (-0.04%)	⬇️
py3.7	86.13% <98.27%> (-0.05%)	⬇️
py3.7_all	99.16% <100.00%> (-0.04%)	⬇️
py3.7_types	99.21% <100.00%> (-0.04%)	⬇️
py3.8	86.33% <98.30%> (-0.04%)	⬇️
py3.8_all	99.33% <100.00%> (-0.04%)	⬇️
py3.8_types	99.36% <100.00%> (-0.04%)	⬇️
py3.9	86.25% <98.30%> (-0.01%)	⬇️
py3.9_all	99.28% <100.00%> (-0.01%)	⬇️
py3.9_types	99.30% <100.00%> (-0.01%)	⬇️

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[sonarcloud]

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