test: add additional tests for extname

[danilofuchs]

Node behavior for extname("file.tar.gz") is .gz

Adding tests to make sure pathe can handle that

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.31%. Comparing base (bdab761) to head (0cbd74b).
Report is 18 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #186      +/-   ##
==========================================
- Coverage   99.45%   99.31%   -0.14%     
==========================================
  Files           4        4              
  Lines         364      293      -71     
  Branches      114      120       +6     
==========================================
- Hits          362      291      -71     
  Misses          2        2              

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[pi0]

Thanks.