Upgrade Validation Actions

[dmtucker]

pytest-mypy/.github/workflows/validation.yml

Lines 10 to 11 in cf649b9

	- uses: actions/checkout@v2
	- uses: actions/setup-python@v2

https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/