fix: ensure compatibility of pdm build --locked with pdm 2.26.2 (fixes RuntimeError: TOMLFile not opened for write)

[sigma67]

closes #29

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.27%. Comparing base (7e81f60) to head (777ee0e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #30      +/-   ##
==========================================
+ Coverage   95.23%   95.27%   +0.03%     
==========================================
  Files           3        3              
  Lines         126      127       +1     
  Branches       20       20              
==========================================
+ Hits          120      121       +1     
  Misses          4        4              
  Partials        2        2              

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