chore: Bump flake8,flake8-isort

- flake8@6.0.0 and later
- flake8-isort@6.0.0 and later

Signed-off-by: Hiroshi Miura <miurahr@linux.com>

pyproject.toml

@@ -58,10 +58,10 @@ test = [
 ]
 check = [
     "mypy>=0.990",
-    "flake8<6",
+    "flake8>=6.0.0,<7.0.0",
     "flake8-black",
     "flake8-colors",
-    "flake8-isort>=5.0.3,<6.0.0",
+    "flake8-isort>=6.0.0,<7.0.0",
     "flake8-pyi",
     "flake8-typing-imports",
     "docutils",