Re: BUG #17036: generated column cann't modifyed auto when update

And immutable function is stable when parameter not change, when parameter changed , the immutable function will recall and recompute.

but in PG 13 and PG 14 , it is also wrong.

```

create or replace function im_now (anyelement) returns timestamptz as $$  

  select now();  

$$ language sql strict immutable; 

create table t1 (id int primary key, c1 int, info text, crt_time timestamp, 

mod_time timestamp GENERATED ALWAYS AS (im_now(t1)) stored);