CI: add lints

.github/workflows/lint.yml

@@ -0,0 +1,8 @@
+name: Lint
+on: [push, pull_request]
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: psf/black@stable

.github/workflows/test.yml

@@ -1,5 +1,5 @@
-name: build docker image and run tests inside
-on: push
+name: Tests
+on: [push, pull_request]
 jobs:
   tests:
     runs-on: ubuntu-latest

.pre-commit-config.yaml

@@ -14,10 +14,11 @@ repos:
     -   id: flake8
     -   id: mixed-line-ending
     -   id: trailing-whitespace
--   repo: https://github.com/pre-commit/mirrors-yapf
-    rev: v0.29.0
+-   repo: https://github.com/psf/black
+    rev: stable
     hooks:
-    -   id: yapf
+    -   id: black
+        language_version: python3
 -   repo: https://github.com/PyCQA/pydocstyle
     rev: 5.0.1
     hooks: