Add :requires_admin tag to skip ff test in production

See https://gitlab.com/gitlab-org/gitlab/-/issues/260283 for details

qa/qa/specs/features/browser_ui/3_create/merge_request/view_merge_request_merge_ref_diff_spec.rb

 # frozen_string_literal: true
 
 module QA
-  RSpec.describe 'Create' do
+  RSpec.describe 'Create', :requires_admin do
     describe 'View merge request merge-ref diff' do
       let(:merge_request) do
         Resource::MergeRequest.fabricate_via_api! do |merge_request|