FIX: add 'noindex' header to rss feed responses.

spec/requests/list_controller_spec.rb

@@ -300,6 +300,7 @@ RSpec.describe ListController do
       get "/latest.rss"
       expect(response.status).to eq(200)
       expect(response.media_type).to eq('application/rss+xml')
+      expect(response.headers['X-Robots-Tag']).to eq('noindex')
     end
 
     it 'renders links correctly with subfolder' do