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]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.84%. Comparing base (4ea0822) to head (df30526).
Report is 12 commits behind head on master.

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

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #37      +/-   ##
==========================================
- Coverage   79.91%   79.84%   -0.08%     
==========================================
  Files           1        1              
  Lines        1125     1131       +6     
==========================================
+ Hits          899      903       +4     
- Misses        226      228       +2     

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[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 ?