Always use the same order specs for `MultiCollectionPaginator`

spec/lib/gitlab/multi_collection_paginator_spec.rb

 require 'spec_helper'
 
 describe Gitlab::MultiCollectionPaginator do
-  subject(:paginator) { described_class.new(Project.all, Group.all, per_page: 3) }
+  subject(:paginator) { described_class.new(Project.all.order(:id), Group.all.order(:id), per_page: 3) }
 
   it 'combines both collections' do
     project = create(:project)