The :const:`Py_TPFLAGS_HAVE_VECTORCALL` flag is now removed from a class
when the class's :py:meth:`~object.__call__` method is reassigned. This
makes vectorcall safe to use with mutable types (i.e. heap types without the
:const:`immutable <Py_TPFLAGS_IMMUTABLETYPE>` flag). Mutable types that do
not override :c:member:`~PyTypeObject.tp_call` now inherit the
:const:`Py_TPFLAGS_HAVE_VECTORCALL` flag.