Toubleshoot codecov failures to upload coverage data

[scorbajio]

This PR looks into issues that codecov is having with uploading coverage info. Currently, only the tx package is reporting coverage in codecov.

This PR was originally at #3375 before it was accidentally closed by resetting and force pushing the head commit.

[scorbajio]

Currently, the logs show codecov-action errors related to token issues, such as here:

[2024-04-25T19:13:10.355Z] ['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: 404 - {'detail': ErrorDetail(string='Unable to locate build via Github Actions API. Please upload with the Codecov repository upload token to resolve issue.', code='not_found')}

Also, a new major version of codecov-action has been released that does not support tokenless uploads.
In order to experiment with fixing the current errors or potentially even just updating to version 4.3.0 of codecov-actions, a codecov token can be used by adding it to github actions secrets.

Some resources on adding the token:

• https://github.com/codecov/codecov-action
• https://docs.codecov.com/docs/adding-the-codecov-token#github-actions
• https://app.codecov.io/gh/ethereumjs/ethereumjs-monorepo/settings