build(actions): update codecov/codecov-action to v4

[gerardroche]

This fixes some deprecations:

tests (3, ubuntu-latest)
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/.