Update codecov versions

[CarloLucibello]

Let's see if I managed to successfully setup codecov for this repo

[CarloLucibello]

It didn't work 😢
I don't know what I did wrong, I followed the instructions
https://app.codecov.io/gh/FluxML/SafeTensors.jl/new

[chengchingwen]

I think you also need to install codecov for this repo https://github.com/apps/codecov

[CarloLucibello]

It seems installed... I don't know what else to do. @ToucheSir any idea?

[ToucheSir]

According to https://app.codecov.io/gh/FluxML/SafeTensors.jl/new (needs login with GitHub first), we need to commit this config to the main branch first.

Also, they recommend this config:

- name: Upload coverage reports to Codecov
  uses: codecov/codecov-action@v4.0.1
  env:
    token: ${{ secrets.CODECOV_TOKEN }}
    slug: FluxML/SafeTensors.jl

Should we add the slug field?

Also also, should we make the CODECOV_TOKEN an org-wide secret like https://discourse.julialang.org/t/psa-new-version-of-codecov-action-requires-additional-setup/109857 suggests? We basically have to repeat this process for every repo that currently uses CodeCov.