Bump flake8 from 3.9.2 to 4.0.1 (#1168)

Author: dependabot[bot]

requirements/requirements_dev.txt

@@ -3,7 +3,7 @@ attrs>=19.2.0
 bandit==1.7.1
 black==21.12b0
 dlint==0.12.0
-flake8==3.9.2
+flake8==4.0.1
 flake8-bandit==2.1.2
 flake8-bugbear==21.4.3
 hypothesis==6.8.9