Fix tuple test

Author: tannewt

py/objtuple.c

@@ -181,7 +181,7 @@ mp_obj_t mp_obj_tuple_binary_op(mp_binary_op_t op, mp_obj_t lhs, mp_obj_t rhs) {
 mp_obj_t mp_obj_tuple_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
     if (value == MP_OBJ_SENTINEL) {
         // load
-        mp_obj_tuple_t *self = MP_OBJ_TO_PTR(self_in);
+        mp_obj_tuple_t *self = mp_instance_cast_to_native_base(self_in, MP_OBJ_FROM_PTR(&mp_type_tuple));
 #if MICROPY_PY_BUILTINS_SLICE
         if (MP_OBJ_IS_TYPE(index, &mp_type_slice)) {
             mp_bound_slice_t slice;