python3.pkgs.bcrypt: fix build

also use pyproject format as we're heading that direction.

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

···
 { lib
 , buildPythonPackage
+, setuptools
 , isPyPy
 , fetchPypi
 , pythonOlder
···
 buildPythonPackage rec {
   pname = "bcrypt";
   version = "3.2.0";
-  format = "setuptools";
+  format = "pyproject";
 
   disabled = pythonOlder "3.6";
 
···
     sha256 = "5b93c1726e50a93a033c36e5ca7fdcd29a5c7395af50a6892f5d9e7c6cfbfb29";
   };
 
+  nativeBuildInputs = [
+    setuptools
+  ];
+
   propagatedBuildInputs = [
     six
-  ] ++ lib.optional (!isPyPy) [
     cffi
   ];
 
-  propagatedNativeBuildInputs = lib.optional (!isPyPy) [
+  propagatedNativeBuildInputs = [
     cffi
   ];