Add black GitHub Action

.github/workflows/black.yml

@@ -0,0 +1,17 @@
+name: Black formatting (79 chars lines)
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+  workflow_dispatch:
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - uses: psf/black@stable
+        with:
+          options: "--check --diff --line-length 79"