Bump flake8 from 3.9.2 to 6.0.0

Bumps [flake8](https://github.com/pycqa/flake8) from 3.9.2 to 6.0.0.
- [Release notes](https://github.com/pycqa/flake8/releases)
- [Commits](PyCQA/flake8@3.9.2...6.0.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

requirements.txt

@@ -13,7 +13,7 @@ twine==4.0.1
 # Testing
 autoflake==1.7.7
 black==22.10.0
-flake8==3.9.2
+flake8==6.0.0
 importlib-metadata==4.13.0; python_version>='3.7'
 isort==5.10.1
 pytest==7.2.0