Bump flake8 from 3.9.2 to 4.0.1

Bumps [flake8](https://github.com/pycqa/flake8) from 3.9.2 to 4.0.1.
- [Release notes](https://github.com/pycqa/flake8/releases)
- [Commits](PyCQA/flake8@3.9.2...4.0.1)

---
updated-dependencies:
- dependency-name: flake8
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -16,7 +16,7 @@ croniter==1.2.0
     # via -r requirements.in
 deprecated==1.2.13
     # via redis
-flake8==3.9.2
+flake8==4.0.1
     # via
     #   -r requirements.in
     #   flake8-isort
@@ -40,9 +40,9 @@ pluggy==1.0.0
     # via pytest
 py==1.11.0
     # via pytest
-pycodestyle==2.7.0
+pycodestyle==2.8.0
     # via flake8
-pyflakes==2.3.1
+pyflakes==2.4.0
     # via flake8
 pyparsing==3.0.7
     # via packaging