BUG #18609: Repeated installcheck failure in test_pg_dump due to existing role

The following bug has been logged on the website:

Bug reference:      18609
Logged by:          Nikita Kalinin
Email address:      n.kalinin@postgrespro.ru
PostgreSQL version: 16.4
Operating system:   ubuntu 22.04
Description:        

Hello! 
When running the installcheck a second time, the test_pg_dump fails due to
the following reason:
CREATE ROLE regress_dump_test_role;
+ERROR:  role "regress_dump_test_role" already exists  
CREATE EXTENSION test_pg_dump;  

This issue is present from REL_12_STABLE to REL_16_STABLE. Maybe it's worth
adding DROP ROLE regress_dump_test_role at the end of the test, like in
REL_17_STABLE?