fix(config): ensure the actually used config file is correct, better test coverage

[bearomorphism]

This is an improvement based on #1773

• Improved test coverage of multiple config file warning
• Ensured the consistency of actually used config file, which is not always the first element of the candidates

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.93%. Comparing base (193859b) to head (fa5a40a).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1784   +/-   ##
=======================================
  Coverage   97.93%   97.93%           
=======================================
  Files          60       60           
  Lines        2611     2612    +1     
=======================================
+ Hits         2557     2558    +1     
  Misses         54       54           

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