BUG #17626: Permission denied errors should list role as well as user

The following bug has been logged on the website:

Bug reference:      17626
Logged by:          Loren Siebert
Email address:      loren@paradigm.xyz
PostgreSQL version: 14.5
Operating system:   Debian
Description:

I'm running this set of commands:
create user elevated_user IN ROLE pg_read_all_data;
create user regular_user;
create table foo (id int);
set role elevated_user;
select * from foo; -- works
set role regular_user;
select * from foo; -- errors

The error message looks like "user=elevated_user ERROR:  permission denied
for table foo".
In fact, that user does have permission to access the table. But the
regular_role it has just assumed does not.
I would suggest that the error message look like "user=elevated_user,
role=regular_user ERROR:  permission denied for table foo"