Github Actions black from PSF

github_actions_black_psf.yml

# .github/workflows/black.yml
name: black -l 79

on: [push]

jobs:
  black:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - uses: actions/setup-python@v2
      - uses: psf/black@stable # the default is equivalent to `black . --diff --check`.
        with:
          args: "application/ -l 79 --check"