FIX allow state_setter to be an arbitrary callable

Author: pierreglaser

Modules/_pickle.c

@@ -3718,7 +3718,7 @@ save_reduce(PicklerObject *self, PyObject *args, PyObject *obj)
 
     if (state_setter == Py_None)
         state_setter = NULL;
-    else if (!PyFunction_Check(state_setter)) {
+    else if (!PyCallable_Check(state_setter)) {
         PyErr_Format(st->PicklingError, "sixth element of the tuple "
                      "returned by __reduce__ must be a function, not %s",
                      Py_TYPE(state_setter)->tp_name);