BUG #17259: RETURN QUERY no longer accepts an UPDATE RETURNING

The following bug has been logged on the website:

Bug reference: 17259
Logged by: Jorge Gualtieri
Email address: jorge(at)jrg(dot)com(dot)br
PostgreSQL version: 14.0
Operating system: Ubuntu 20.04.3 LTS
Description:

In version 14.0 RETURN QUERY with UPDATE RETURNING in a function is
reporting an error and it works in version 13.4.
Test code:
--
create table test (i int primary key, j int);
insert into test values (1,1);

create or replace function f_test() returns setof int
language plpgsql
as $fn$
begin
return query
update test
set j = j+1
where i = 1
returning j;

end;
$fn$;

select * from f_test();
--
ERROR: 42601: query is not a SELECT
CONTEXT: query: update test
set j = j+1
where i = 1
returning j
PL/pgSQL function f_test() line 3 at RETURN QUERY
LOCATION: exec_stmt_return_query, pl_exec.c:3571