psql: Add test for handling of replication commands
Add a test for the clean handling of unsupported replication command
responses. This was once accidentally broken, and it seems unusual
enough that it's easy to forget when testing manually.
Discussion: https://www.postgresql.org/message-id/
2570e2ae-fa0f-aac9-f72f-
bb59a9983a20@enterprisedb.com