Update pep8-naming compatibility with flake8

`pep8-naming` tests fail for `flake8` v3/v4; avoid suggesting that it works.

Signed-off-by: Stavros Ntentos <11300730-stavros-relex@users.noreply.gitlab.com>

requirements.txt

@@ -0,0 +1 @@
+flake8>=5.0.0,<6.0.0

setup.cfg

@@ -3,3 +3,6 @@ project_urls =
     Source=https://github.com/PyCQA/pep8-naming
     Issues=https://github.com/PyCQA/pep8-naming/issues
     Changelog=https://github.com/PyCQA/pep8-naming/blob/main/CHANGELOG.rst
+
+[options]
+install_requires = file: requirements.txt

setup.py

@@ -42,7 +42,6 @@ def run_tests(self):
     license='Expat license',
     package_dir={'': 'src'},
     py_modules=['pep8ext_naming'],
-    install_requires=['flake8>=3.9.1'],
     zip_safe=False,
     python_requires='>=3.7',
     entry_points={

tox.ini

@@ -1,5 +1,11 @@
 [tox]
-envlist = py37,py38,py39,py310,py310-flake8,pypy3
+envlist =
+    py37-flake8{5,6},
+    py38-flake8{5,6},
+    py39-flake8{5,6},
+    py310-flake8{5,6},
+    py310-flake8,
+    pypy3
 
 [gh-actions]
 python =
@@ -12,7 +18,8 @@ python =
 [testenv]
 commands = python run_tests.py
 deps =
-    flake8 >= 5.0.0
+    flake85: flake8 >= 5.0.0, < 6.0.0
+    flake86: flake8 >= 6.0.0, < 7.0.0
 
 [testenv:py310-flake8]
 basepython = python3.10