Backport EE changes for the schema specs

This backports two EE specific changes made to the schema changes. We do
not yet backport the EE prepend, as this will/can be done when
https://gitlab.com/gitlab-org/gitlab-ce/issues/58170 is implemented.

spec/db/schema_spec.rb

 # frozen_string_literal: true
 
 require 'spec_helper'
-require Rails.root.join('ee', 'spec', 'db', 'schema_support')
+require Rails.root.join('ee', 'spec', 'db', 'schema_support') if Gitlab.ee?
 
 describe 'Database schema' do
   prepend ::EE::DB::SchemaSupport