actions/checkout fails with: ref: ${{ github.event.pull_request.head.sha }} with un-pushed commits

[brianjmurrell]

If I have a step:

      - name: Checkout code
        uses: actions/checkout@v4
        with:
          ref: ${{ github.event.pull_request.head.sha }}

When I have local commits that I have not pushed remotely, the checkout action fails since github.event.pull_request.head.sha doesn't exist on GitHub yet, as I have not pushed it.

How do I simulate a checkout on the code that is only in my local repo? I.e. that I have not yet pushed.

Surely I don't have to push my local commits. The entire point of using act is to test my code locally before pushing it.

Reference: https://github.com/actions/checkout/blob/v3.0.2/README.md#checkout-pull-request-head-commit-instead-of-merge-commit