docs: bump upload-artifact version

[dunglas]

The current version is outdated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 69.23%. Comparing base (14707cd) to head (4b18fb2).
Report is 25 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #479      +/-   ##
==========================================
+ Coverage   66.92%   69.23%   +2.30%     
==========================================
  Files           3        3              
  Lines         130      130              
  Branches       23       30       +7     
==========================================
+ Hits           87       90       +3     
- Misses         27       36       +9     
+ Partials       16        4      -12     

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[caarlos0]

thanks!