[stable5.0] ci(package): bump deprecated upload-artifact action to v4

[st3iny]

Version 3 was deprecated some time ago and now fails automatically: https://github.com/nextcloud/calendar/actions/runs/13111311455/job/36575672626?pr=6692

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 15.40%. Comparing base (7508abb) to head (36d1f0f).
Report is 10 commits behind head on stable5.0.

Additional details and impacted files

@@            Coverage Diff             @@
##           stable5.0    #6695   +/-   ##
==========================================
  Coverage      15.40%   15.40%           
==========================================
  Files            206      206           
  Lines           9458     9458           
  Branches        2206     2195   -11     
==========================================
  Hits            1457     1457           
- Misses          7682     7683    +1     
+ Partials         319      318    -1     

Flag	Coverage Δ
javascript	15.40% <ø> (ø)

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