Fix fail-fast job when there are migrations present

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/101613
consolidated some of the logic for calling `schema_migrate_down!` to
`spec/support/multiple_databases.rb`, but it introduced some issues
with database cleanup. It appears calling
`with_reestablished_active_record_base` disconnects connections and
clears attribute methods. We now need to:

1. Ensure that tables are deleted before we migrate.
2. Force a refresh of attribute methods after ensuring migrations are
up.

Relates to https://gitlab.com/gitlab-org/gitlab/-/issues/378582