Uses spec_helper instead of rails_helper

spec/rails_helper.rb was removed on
1068ec2e

spec/lib/gitlab/anonymous_session_spec.rb

 # frozen_string_literal: true
-require 'rails_helper'
+require 'spec_helper'
 describe Gitlab::AnonymousSession, :clean_gitlab_redis_shared_state do
   let(:default_session_id) { '6919a6f1bb119dd7396fadc38fd18d0d' }