build: Update codecov and use token

[arbrandes]

Update codecov to the latest version and start using the org-wide token for uploads.

See openedx/wg-frontend#179

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 53.14%. Comparing base (7303f79) to head (d92beb7).
Report is 8 commits behind head on master.

❗ Current head d92beb7 differs from pull request most recent head 6be4aa3

Please upload reports for the commit 6be4aa3 to get more accurate results.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #442   +/-   ##
=======================================
  Coverage   53.14%   53.14%           
=======================================
  Files          80       80           
  Lines        2021     2021           
  Branches      368      362    -6     
=======================================
  Hits         1074     1074           
  Misses        914      914           
  Partials       33       33           

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