FIX: use correct validation method name for default_categories_normal. (#20801)

When we renamed the `default_categories_regular` to `default_categories_normal` we missed a site setting validation method. It allowed the duplicate category ids in `default_categories_normal` site setting and caused the problem in user registration process.

5176c689e9

spec/lib/site_settings/validations_spec.rb

@@ -28,6 +28,10 @@ RSpec.describe SiteSettings::Validations do
       expect { SiteSetting.default_categories_tracking = "#{category.id}" }.to raise_error(
         Discourse::InvalidParameters,
       )
+
+      expect { SiteSetting.default_categories_normal = "#{category.id}" }.to raise_error(
+        Discourse::InvalidParameters,
+      )
     end
   end