chore: fix codecov coverage upload

[jansegre]

Motivation

Codecov's upload task on CI broke, it used to be unstable so we suspected that was the case but apparently it is now required to use a token.

Acceptance Criteria

• Add a secret token to the repo's settings
• Add CI config to expose the token to codecov's upload task

Checklist

• If you are requesting a merge into master, confirm this code is production-ready and can be included in future releases as soon as it gets merged

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 84.88%. Comparing base (adc0191) to head (9a72f60).
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1005      +/-   ##
==========================================
- Coverage   85.10%   84.88%   -0.23%     
==========================================
  Files         296      296              
  Lines       22909    22872      -37     
  Branches     3449     3460      +11     
==========================================
- Hits        19497    19414      -83     
- Misses       2732     2772      +40     
- Partials      680      686       +6     

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