Fix typo in .gitattributes

[VincentLanglet]

Hi @localheinz,
there is a small typo in the gitattribute file.

The test folder is test and not tests.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (4ca8dd4) to head (01e2d34).
Report is 29 commits behind head on master.

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Additional details and impacted files

@@             Coverage Diff             @@
##              master      #275   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
  Complexity        57        57           
===========================================
  Files              6         6           
  Lines            157       154    -3     
===========================================
- Hits             157       154    -3     

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[localheinz]

Thank you, @VincentLanglet!