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 friendly-lamington-fb5690 canceled.

Name	Link
🔨 Latest commit	861b562
🔍 Latest deploy log	https://app.netlify.com/sites/friendly-lamington-fb5690/deploys/662ae806391a860008d813c8

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 57.25%. Comparing base (e56b06e) to head (861b562).
Report is 18 commits behind head on main.

Additional details and impacted files

@@ Coverage Diff @@## main #547 +/- ##
==========================================
- Coverage 57.47% 57.25% -0.22% 
==========================================
Files 11 11 Lines 729 737 +8 Branches 35 36 +1 ==========================================
+ Hits 419 422 +3 - Misses 310 315 +5 

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