Use ruff instead of flake8. (#15)

ruff is significantly faster than flake8 and covers a superset
of the same linting checks.

Author: clokep

.github/workflows/python-poetry-ci.yml

@@ -33,8 +33,8 @@ jobs:
       - name: Code style (black)
         run: poetry run black --check --diff .
 
-      - name: Semantic checks (flake8)
-        run: poetry run flake8
+      - name: Semantic checks (ruff)
+        run: poetry run ruff .
 
   mypy:
     runs-on: ubuntu-latest