Multihost bug when working with SqlAlchemy

• asyncpg version: 0.24.0
• PostgreSQL version: 10
• Do you use a PostgreSQL SaaS? If so, which? Can you reproduce
  the issue with a local PostgreSQL install?:
• Python version: 3.9.6
• Platform: Doesn't matter
• Do you use pgbouncer?: No
• Did you install asyncpg with pip?: Yes
• If you built asyncpg locally, which version of Cython did you use?:
• Can the issue be reproduced under both asyncio and
  uvloop?: doesn't matter

When we use asyncpg via sqlalchemy, we pass a dsn string to sqlalchemy and it parses this string and call asyncpg connect with host, port, username and etc instead of dsn. And it looks like asyncpg can't handle multiple hosts, separated by commas, passed in host param.

Comienza rastreando cómo SQLAlchemy analiza el DSN y llama a asyncpg con el parámetro host, y luego reproduce el caso con varios hosts de PostgreSQL separados por comas usando las versiones indicadas. Se considera terminado cuando el comportamiento de conexión multihost funciona al pasar SQLAlchemy el valor host analizado a asyncpg.