build.yaml: Fix extraction of artifacts when preparing for release

[hjpotter92]

https://discord.com/channels/423160867534929930/1275180318474895420

This should fix the issue during release step, where downloaded artifacts are being placed inside nested sub-directory since we bumped to upload-artifacts@v4.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 57.34447%. Comparing base (84d88af) to head (6f21344).
Report is 2 commits behind head on master.

Additional details and impacted files

@@                 Coverage Diff                 @@
##              master       #3146         +/-   ##
===================================================
- Coverage   57.35266%   57.34447%   -0.00819%     
===================================================
  Files             92          92                 
  Lines          15797       15801          +4     
===================================================
+ Hits            9060        9061          +1     
- Misses          6133        6136          +3     
  Partials         604         604                 

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