test: add missing file close

[alessio-perugini]

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What kind of change does this PR introduce?

Missing file close

What is the current behavior?

What is the new behavior?

Does this PR introduce a breaking change, and is titled accordingly?

Other information

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (95753fc) 68.85% compared to head (2bf2f58) 68.85%.
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2492   +/-   ##
=======================================
  Coverage   68.85%   68.85%           
=======================================
  Files         204      204           
  Lines       20465    20465           
=======================================
  Hits        14091    14091           
  Misses       5220     5220           
  Partials     1154     1154           

Flag	Coverage Δ
unit	68.85% <ø> (ø)

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[cmaglie]

Actually, you can replace the whole createConfig function with the *Path.WriteFile method.