By default, this is equivalent to running `git fetch` and `git checkout $GITHUB_SHA`, so that you'll always have your repo contents at the version that triggered the workflow.
By default, the branch or tag ref that triggered the workflow will be checked out. If you wish to check out a different branch, a different repository or use different token to checkout, specify that using `with.ref`, `with.repository` and `with.token`.
> - `${{ github.token }}` is scoped to the current repository, so if you want to checkout another repository that is private you will need to provide your own [PAT](https://help.github.com/en/github/authenticating-to-github/creating-a-personal-access-token-for-the-command-line).
> - Private submodules must be configured via `https` not `ssh`.
> - `${{ github.token }}` only has permission to the workflow triggering repository. If the repository contains any submodules that come from private repositories, you will need to add your [PAT](https://help.github.com/en/github/authenticating-to-github/creating-a-personal-access-token-for-the-command-line) as secret and use the secret in `with.token` to make the `checkout` action work.
For more details, see [Contexts and expression syntax for GitHub Actions](https://help.github.com/en/articles/contexts-and-expression-syntax-for-github-actions) and [Creating and using encrypted secrets](https://help.github.com/actions/automating-your-workflow-with-github-actions/creating-and-using-encrypted-secrets)