Bump flake8 from 3.8.4 to 4.0.1 (#391)

Bumps [flake8](https://github.com/pycqa/flake8) from 3.8.4 to 4.0.1.
- [Release notes](https://github.com/pycqa/flake8/releases)
- [Commits](PyCQA/flake8@3.8.4...4.0.1)

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

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements-dev.txt

@@ -7,7 +7,7 @@ pytest-runner==5.2
 pytest-flakes==4.0.4
 pytest-pylint==0.18.0
 pytest-sugar==0.9.4
-flake8==3.8.4
+flake8==4.0.1
 selenium==4.0.0
 docutils==0.16
 pygments==2.10.0