build: upgrade codecov from v3 to v4, use secret

[kdmccormick]

Per https://openedx.atlassian.net/wiki/spaces/COMM/pages/3438280709/Adding+Codecov, I think this is the right thing to do.

@dcoa , could you review this?

[kdmccormick]

Hm, the Run Coverage step says:

Error: Codecov token not found. Please provide Codecov token with -t flag.

[dcoa]

There is a second file that uses codecov too, manual-publish.yml

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 83.41%. Comparing base (de09872) to head (877f51f). Report is 19 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #692      +/-   ##
==========================================
- Coverage   83.50%   83.41%   -0.10%     
==========================================
  Files          40       40              
  Lines        1073     1073              
  Branches      197      197              
==========================================
- Hits          896      895       -1     
- Misses        165      166       +1     
  Partials       12       12              

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[kdmccormick]

@dcoa how does this look?