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, specify that using `with.ref`:
For more details, see [Contexts and expression syntax for GitHub Actions](https://help.github.com/en/articles/contexts-and-expression-syntax-for-github-actions)