Fix "__Pyx_PyObject_CallOneArg()" when calling PyCFunctions with the METH_METHOD flag set.

Cython/Utility/ObjectHandling.c

@@ -2271,7 +2271,7 @@ static CYTHON_INLINE PyObject* __Pyx_PyObject_CallOneArg(PyObject *func, PyObjec
             // fast and simple case that we are optimising for
             return __Pyx_PyObject_CallMethO(func, arg);
 #if CYTHON_FAST_PYCCALL
-        } else if (PyCFunction_GET_FLAGS(func) & METH_FASTCALL) {
+        } else if (__Pyx_PyFastCFunction_Check(func)) {
             return __Pyx_PyCFunction_FastCall(func, &arg, 1);
 #endif
         }