Replace _PyList_Extend with PyList_SetSlice

This private function is no longer exported in Python 3.13.

It is possible that a PyList_Extend() function-like macro may be added
before Python 3.13 final, but using PyList_SetSlice() directly will
still work.

python/cpython#108451

python/cpython#111138

pvectorcmodule.c

@@ -1313,7 +1313,7 @@ static PyObject *PVectorEvolver_append(PVectorEvolver *self, PyObject *args) {
 }
 
 static PyObject *PVectorEvolver_extend(PVectorEvolver *self, PyObject *args) {
-  PyObject *retVal = _PyList_Extend((PyListObject *)self->appendList, args);
+  PyObject *retVal = PyList_SetSlice((PyListObject *)self->appendList, PY_SSIZE_T_MAX, PY_SSIZE_T_MAX, args);
   if (retVal == NULL) {
     return NULL;
   }