Fix test when PGSSLMODE=disable
Fix test when PGSSLMODE=disable

When PGSSLMODE=disable no fallback config was created which would cause
the check that fallbacks are deep copied to crash on:

copied.Fallbacks[0].Port = uint16(5433)

jackc/pgx,jackc/pgx,jackc/pgconn,jackc/pgx,jackc/pgx,jackc/pgconn