Describe the bug

https://github.com/pyca/cryptography/pull/5652/checks?check_run_id=1571744687

      - name: Setup python
        uses: actions/setup-python@v2
        with:
          python-version: ${{ matrix.PYTHON.VERSION }}

->

Error: IS_WINDOWS is not defined

Which version of the action are you using?

• v1
• v2
• Some other tag (such as v2.0.1 or master)

Environment

• self-hosted
• Linux
• Windows
• Mac

If applicable, please specify if you're using a container

Python Versions

pypy3

Run/Repo Url
https://github.com/pyca/cryptography/pull/5652/checks?check_run_id=1571744687