test(pool): verify the overriding of `close()` to act as `putconn()`

test(pool): verify the overriding of `close()` to act as `putconn()`

We would like to maintain this possibility on a best-effort basis. The
hack has been mentioned in #1046 and upstream in
https://github.com/sqlalchemy/sqlalchemy/discussions/12522 and is useful
to integrate psycopg pool with the SQLAlchemy NullPool.