Bump flake8 from 3.8.4 to 3.9.2

Bumps [flake8](https://gitlab.com/pycqa/flake8) from 3.8.4 to 3.9.2.
- [Release notes](https://gitlab.com/pycqa/flake8/tags)
- [Commits](https://gitlab.com/pycqa/flake8/compare/3.8.4...3.9.2)

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

Author: dependabot-preview[bot]

requirements.txt

@@ -13,7 +13,7 @@ moderngl==5.6.4
 pyrr==0.10.3
 pyrender==0.1.45
 pytest-xvfb==2.0.0
-flake8==3.8.4
+flake8==3.9.2
 flake8-quotes==3.2.0
 radon==4.5.2