The `rake db:seed` command was broken for the primary environment if the
application is using multiple databases. We never implemented `rake
db:seed` for other databases (coming soon), but that shouldn't break the
default case.

The reason this was broken was because `abort_if_pending_migrations`
would loop through the configs for all databases and check for
migrations but would leave the last established connection. So `db:seed`
was looking in the wrong database for the table to seed.

This PR doesn't fix the fact that `db:seed` doesn't work for multiple
databases but does fix the default case.

Fixes #36817
Co-authored-by: NJohn Crepezzi <john.crepezzi@gmail.com>