No error thrown when CTE columns updated in updates set clause

Bug found while testing MDEV-37220 (Merged into main branch 12.3.0)

CTE's are read only i.e It cannot have their columns updated in updates set clause
Attempting to do so , should throw error
ERROR 1288 (HY000): The target table cte of the UPDATE is not updatable

Issue :
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No error thrown when cte columns are updated in update clause (When there is subquery in SET clause )

MariaDB [m]> with cte as (select * from t1 where c < 5) update cte set cte.a =(select a from cte);

Query OK, 0 rows affected (0.002 sec)

Rows matched: 1  Changed: 0  Warnings: 0

Note:

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For literal values ,it throws error as expected
MariaDB [m]> with cte as (select * from t1 where c < 5) update cte set cte.a =10;
ERROR 1288 (HY000): The target table cte of the UPDATE is not updatable

How to repro:

create table t1(a int ,b int, c int);

insert into t1 values (1,1,10) , (2,3,1);

create table t3(a int);

insert into t3 values (1),(2);

with cte as (select * from t1 where c < 5) update cte set cte.a =(select a from cte);