updates to codecov action

[k-doering-NOAA]

addresses #122. More context in NOAA-FIMS/FIMS#605.

I tested these changes on a branch in FIMS. I made sure:

• You could add a token to the workflow and it would successfully upload to codecov.io.
• If no token was provided, the user gets an error message that tells them exactly what is wrong:
  ![screenshot showing the error message](https://github.com/nmfs-fish-tools/ghactions4r/assets/48930335/adfff28e-d1d0-460a-82d8-a93d7ddf56dd

I'm wondering if I should check that the workflow fails if the upload is unsuccessful? Unfortunately, it did not, which lead to this issue not being caught quickly.

I should also note that once this change is pushed to main, I think all workflows that depend on it will fail due to the lack of a token, so this may need more documentation to help users make the changes required.

In particular, all user will need to add the upload token from codecov.io to a GitHub secret, then add the secret to the workflow yaml (or more simply, delete their caller workflow and run use_calc_coverage() again). Below is a snippet of the jobs section of the caller workflow:

jobs:
  call-workflow:
    uses: nmfs-fish-tools/ghactions4r/.github/workflows/calc-coverage.yml@main
    secrets:
      CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}

I also made edits to the vignette, as I don't think this workflow is general to use for codecov and coveralls anymore, unfortunately.

[Bai-Li-NOAA]

Looks good to me!