Add have_cacheable_headers matcher for responses (#31727)

spec/requests/custom_stylesheets_spec.rb

@@ -9,11 +9,10 @@ describe 'Custom stylesheets' do
     it 'returns http success' do
       expect(response)
         .to have_http_status(200)
+        .and have_cacheable_headers
         .and have_attributes(
           content_type: match('text/css')
         )
     end
-
-    it_behaves_like 'cacheable response'
   end
 end