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 97.97%. Comparing base (bd02381) to head (7ae6414).
⚠️ Report is 2 commits behind head on next-release.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@               Coverage Diff                @@
##           next-release    #1803      +/-   ##
================================================
- Coverage         97.98%   97.97%   -0.01%     
================================================
  Files                60       60              
  Lines              2678     2673       -5     
================================================
- Hits               2624     2619       -5     
  Misses               54       54              

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[Lee-W]

a few nits