BUG #19637: pg_event_trigger_ddl_commands can't process GRANT ON PROPERTY GRAPH

The following bug has been logged on the website:

Bug reference: 19637
Logged by: Alexander Lakhin
Email address: exclusion(at)gmail(dot)com
PostgreSQL version: 19beta3
Operating system: Ubuntu 24.04
Description:

The following script:
CREATE OR REPLACE FUNCTION event_trigger_report_end()
RETURNS event_trigger
LANGUAGE plpgsql
AS $$
DECLARE r RECORD;
BEGIN
FOR r IN SELECT * FROM pg_event_trigger_ddl_commands()
LOOP
RAISE NOTICE 'END: command_tag=% type=% identity=%',
r.command_tag, r.object_type, r.object_identity;
END LOOP;
END; $$;
CREATE EVENT TRIGGER regress_event_trigger_report_end ON ddl_command_end
EXECUTE PROCEDURE event_trigger_report_end();

CREATE PROPERTY GRAPH pg;
GRANT SELECT ON PROPERTY GRAPH pg TO public;

fails with:
ERROR: XX000: unsupported object type: 30
CONTEXT: PL/pgSQL function event_trigger_report_end() line 4 at FOR over
SELECT rows
LOCATION: stringify_grant_objtype, event_trigger.c:2335

Reproduced starting from 2f094e7ac.