Update python-app.yml

install flake8 directly.
Will incorporate in pyproject.toml and then revert

.github/workflows/python-app.yml

@@ -36,6 +36,7 @@ jobs:
  poetry install -E all
  - name: Lint with flake8
  run: |
+ pip install flake8
  # stop the build if there are Python syntax errors or undefined names
  flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics
  # exit-zero treats all errors as warnings. The GitHub editor is 127 chars wide