chore(deps): bump flake8 from 3.9.0 to 3.9.2

Bumps [flake8](https://gitlab.com/pycqa/flake8) from 3.9.0 to 3.9.2.
- [Release notes](https://gitlab.com/pycqa/flake8/tags)
- [Commits](https://gitlab.com/pycqa/flake8/compare/3.9.0...3.9.2)

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

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

requirements_test.txt

@@ -1,5 +1,5 @@
 pylint==2.7.2
 isort==5.8.0
-flake8==3.9.0
+flake8==3.9.2
 mypy==0.812
 black==21.7b0