DEV: Unify way to reset Site.preloaded_category_custom_fields (#17384)

spec/models/site_spec.rb

@@ -133,7 +133,7 @@ describe Site do
 
       expect(categories.last[:custom_fields]["enable_marketplace"]).to eq('f')
     ensure
-      Site.preloaded_category_custom_fields.clear
+      Site.reset_preloaded_category_custom_fields
     end
 
     it 'sets the can_edit field for categories correctly' do

spec/requests/api/site_spec.rb

@@ -34,7 +34,7 @@ describe 'site' do
             let(:expected_request_schema) { expected_request_schema }
           end
         ensure
-          Site.preloaded_category_custom_fields = Set.new
+          Site.reset_preloaded_category_custom_fields
         end
       end
     end

spec/serializers/site_serializer_spec.rb

@@ -25,7 +25,7 @@ describe SiteSerializer do
 
     expect(c1[:custom_fields]["enable_marketplace"]).to eq("t")
   ensure
-    Site.preloaded_category_custom_fields.clear
+    Site.reset_preloaded_category_custom_fields
   end
 
   it "includes category tags" do