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](https://github.com/pycqa/flake8/compare/3.9.2...4.0.1)
---
updated-dependencies:
- dependency-name: flake8
dependency-type: direct:development
update-type: version-update:semver-major
...
Signed-off-by: dependabot[bot] <support@github.com>