Add codecov token

[yuxincs]

We have upgraded our codecov upload action to v4. However, tokenless uploads are unsupported now (see codecov/codecov-action#1293). This PR fixes the config to give the action a codecov token stored in repository secrets.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.09%. Comparing base (3fc9b8a) to head (198b3d2).
Report is 13 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #921      +/-   ##
============================================
+ Coverage     86.98%   87.09%   +0.10%     
- Complexity     1959     1990      +31     
============================================
  Files            77       77              
  Lines          6330     6430     +100     
  Branches       1223     1245      +22     
============================================
+ Hits           5506     5600      +94     
- Misses          420      422       +2     
- Partials        404      408       +4     

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

[msridhar]

LGTM thanks for the fix!