BUG #15631: Generated as identity field in a temporary table with on commit drop corrupts system catalogs

The following bug has been logged on the website:

Bug reference:      15631
Logged by:          Serge Latyntsev
Email address:      dnsl48@gmail.com
PostgreSQL version: 11.1
Operating system:   Alpine
Description:

When using `generated by default as identity` in a temporary table with `on
commit drop`, but without starting a transaction, system catalogs get
corrupted and won't let create temporary tables anymore.

Here's how to reproduce (within a docker container):

$ docker exec -it $(docker run -d --rm postgres:11.1-alpine) bash
# psql postgres postgres
# create temporary table foo ( bar int generated by default as identity ) on
commit drop;
CREATE TABLE
# \q
# psql postgres postgres 
# create temporary table a (b varchar);
ERROR:  could not open relation with OID 16388
LINE 1: create temporary table a (b varchar);