[actions] Add CODECOV_TOKEN secret for uploads

[codecov[bot]]

Codecov Report

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

Project coverage is 88.89%. Comparing base (4092157) to head (cd64812). Report is 5 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #3478 +/- ## ======================================= Coverage 88.89% 88.89% ======================================= Files 254 254 Lines 14081 14081 ======================================= + Hits 12517 12518 +1 + Misses 1564 1563 -1 ```

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