pypy3Packages.pycodestyle: disable broken test (#412921)

pkgs/development/python-modules/pycodestyle/default.nix

···
   python,
   pytestCheckHook,
   setuptools,
+  isPyPy,
 }:
 
 buildPythonPackage rec {
···
   postCheck = ''
     ${python.interpreter} -m pycodestyle --statistics pycodestyle.py
   '';
+
+  disabledTests = lib.optionals isPyPy [
+    # PyPy reports a SyntaxError instead of ValueError
+    "test_check_nullbytes"
+  ];
 
   meta = with lib; {
     changelog = "https://github.com/PyCQA/pycodestyle/blob/${version}/CHANGES.txt";