WIP: CI: Update Codecov Action

[un-def]

https://github.com/codecov/codecov-action/releases/tag/v4.0.0

v4 no longer supports tokenless uploading, but this feature is all but broken due to rate limits, the last successful upload was three month ago: https://app.codecov.io/gh/luarocks/hererocks/commit/4ea0822c30c4ed568d6cb43038224b93aae436f4

For example, https://github.com/luarocks/hererocks/actions/runs/9379552301/job/25824719887

[2024-06-05T06:57:06.318Z] ['error'] There was an error running the uploader: Error uploading to https://codecov.io: Error: There was an error fetching the storage URL during POST: 429 - {'detail': ErrorDetail(string='Rate limit reached. Please upload with the Codecov repository upload token to resolve issue. Expected time to availability: 876s.', code='throttled')}

Alfo fixes the following warning:

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: codecov/codecov-action@v3. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

[codecov-commenter]

Codecov Report

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

Project coverage is 79.64%. Comparing base (4ea0822) to head (b71233b). Report is 7 commits behind head on master.

:exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #37 +/- ## ========================================== - Coverage 79.91% 79.64% -0.27% ========================================== Files 1 1 Lines 1125 1130 +5 ========================================== + Hits 899 900 +1 - Misses 226 230 +4 ```

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

[un-def]

@hishamhm could you please add the Covecov token from Codecov settings https://app.codecov.io/gh/luarocks/hererocks/settings to this repository as the CODECOV_TOKEN repository secret https://github.com/luarocks/hererocks/settings/secrets/actions ?