Polishing Buildkite pipeline

[quffaro]

Removed the $DEPOT variable, which is exported in the build template on .github, so it has no need to be defined locally.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.24%. Comparing base (31938a6) to head (414cd84).
Report is 48 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #85      +/-   ##
==========================================
+ Coverage   86.72%   90.24%   +3.51%     
==========================================
  Files          13       18       +5     
  Lines         889     1179     +290     
==========================================
+ Hits          771     1064     +293     
+ Misses        118      115       -3     

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