should all not-null constraints be inherited?

Hello,

This is how one can create a parent with a non-nullable column and a 
child with the same column nullable:

create table t1(a int not null);
create table t2() inherits (t1);
alter table t2 alter column a drop not null;
insert into t2 select null;

pg_dump produces a dump that fails to restore, as the change by the 
alter command doesn't get addressed.
Reproduced in 10 and 14devel.

Should we fix ALTER TABLE or pg_dump?

Best, Alex