Add flake package to project deps and set up git flow runner

Author: shorodilov

.github/workflows/linter.yml

@@ -23,5 +23,7 @@ jobs:
         run: |
           python -m pip install --upgrade pip
           pip install tox tox-gh-actions
-      - name: Run tox
+      - name: Run pylint
         run: tox -e pylint
+      - name: Run flake8
+        run: tox -e flake8