ci: add codecov token

[danielroe]

with v4 of the codecov action, we need to supply a codecov token (pointed out by @ricardogobbosouza). I've added the token in GH variables...

[netlify]

✅ Deploy Preview for pedantic-sinoussi-65c819 canceled.

Name	Link
🔨 Latest commit	4b721bd
🔍 Latest deploy log	https://app.netlify.com/sites/pedantic-sinoussi-65c819/deploys/662ae7bb16ea900008307394

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.21%. Comparing base (dbd45b4) to head (4b721bd).
Report is 9 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #197   +/-   ##
=======================================
  Coverage   67.21%   67.21%           
=======================================
  Files           7        7           
  Lines         305      305           
  Branches       27       27           
=======================================
  Hits          205      205           
+ Misses         94       92    -2     
- Partials        6        8    +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.