Test logging in via the Authentiq OAuth provider in a feature spec.

- The `migration:path-pg` build was previously failing when the Authentiq
  feature spec was enabled by placing Authentiq configuration in the `test`
  section of `gitlab.yml`

- The `migration:path-pg` task checks out an old revision of the
  codebase (`v8.14.10`) and runs a `schema:load`. It then checks out the commit
  under test, and runs `db:migrate`, to verify that migrations run without
  errors.

- The problem here is that `v8.14.10` does not have the Authentiq module
  installed, but is run with the `gitlab.yml` for `master`, which would contain
  the `Authentiq` configuration in the `test` section.

- The solution was to use the `v8.14.10` `gitlab.yml` for the `schema:load`,
  rather than the `gitlab.yml` from master.