This test was incorrect. `primary` was winning for the schema cache load
but when you boot an application it's actually the first configuration
that wins (in a multi db app).

The test didn't catch this because I forgot to add a migrations_paths to
the configuration.

We updated the schema cache loader railtie as well because any
application that didn't have a `primary` config would not be able to use
the schema cache. Originally we thought we'd enforce a `primary`
configuration but no longer feel that's correct. It's simpler to say
that the first wins in a 3-tier rather than implementing a solution to
require `primary` and / or allow aliases.
Co-authored-by: NJohn Crepezzi <john.crepezzi@gmail.com>
Co-authored-by: NJohn Hawthorn <john@hawthorn.email>