fix(config): include pyproject.toml in multi config file warning

[bearomorphism]

I just remembered that we already have a feature that detects if a configuration file is valid. We can include pyproject.toml in the multi config warning.

Relate #1702

Also added a test to ensure that no warning when there are both pyproject.toml (without cz settings section) and cz.toml

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.95%. Comparing base (cdaa941) to head (5eb1e1c).
⚠️ Report is 1 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1803      +/-   ##
==========================================
- Coverage   97.96%   97.95%   -0.01%     
==========================================
  Files          60       60              
  Lines        2648     2643       -5     
==========================================
- Hits         2594     2589       -5     
  Misses         54       54              

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