flake8のバージョンを固定する

Author: massongit

Pipfile

@@ -12,7 +12,7 @@ requests-mock = "==1.10.0"
 pylint = "==2.15.6"
 sqlfluff = "==1.4.2"
 mypy = "==0.991"
-flake8 = "*"
+flake8 = "==6.0.0"
 black = "*"
 isort = "*"
 pre-commit = "*"