bpo-36974: rename _FastCallKeywords -> _Vectorcall (GH-13653)

diff --git a/Include/descrobject.h b/Include/descrobject.h
index 3db0963..d711485 100644
--- a/Include/descrobject.h
+++ b/Include/descrobject.h
@@ -92,7 +92,7 @@
                                                struct PyGetSetDef *);
 #ifndef Py_LIMITED_API
 
-PyAPI_FUNC(PyObject *) _PyMethodDescr_FastCallKeywords(
+PyAPI_FUNC(PyObject *) _PyMethodDescr_Vectorcall(
         PyObject *descrobj, PyObject *const *args, size_t nargsf, PyObject *kwnames);
 PyAPI_FUNC(PyObject *) PyDescr_NewWrapper(PyTypeObject *,
                                                 struct wrapperbase *, void *);