Use forward slashes for relative paths in config

[imagejan]

By using Path.as_posix(), we ensure forward slashes independent of the platform.

This should help for interoperability between Windows and Linux systems.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.20%. Comparing base (aec9f31) to head (c2264de).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #225   +/-   ##
=======================================
  Coverage   93.20%   93.20%           
=======================================
  Files          65       65           
  Lines        4149     4149           
  Branches      264      264           
=======================================
  Hits         3867     3867           
  Misses        265      265           
  Partials       17       17           

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