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-tests.txt

@@ -1,6 +1,6 @@
 -r requirements.txt
 pytest==7.2.0
 pytest-cov==4.0.0
-flake8==5.0.4
+flake8==6.0.0
 pyflakes==2.5.0
 bump2version==1.0.1