ci: fix missing CODECOV_TOKEN for codecov/codecov-action@v4

[aofei]

For goplus/gop#1822

---

‼️ Steps that must be done before merging:

1. Obtain the upload token (CODECOV_TOKEN) from https://codecov.io/github/goplus/yap/settings
2. Add CODECOV_TOKEN as a repository secret at https://github.com/goplus/yap/settings/secrets/actions

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.38%. Comparing base (36cea50) to head (8d5a425).
Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #112   +/-   ##
=======================================
  Coverage   90.38%   90.38%           
=======================================
  Files          10       10           
  Lines         104      104           
=======================================
  Hits           94       94           
  Misses         10       10           

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