UX: Change wording for 'regular' categories to 'normal' (#17134)

At some point in the past we decided to rename the 'regular' notification state of topics/categories to 'normal'. However, some UI copy was missed when the initial renaming was done so this commit changes the spots that were missed to the new name.

spec/lib/topic_query_spec.rb

@@ -549,7 +549,7 @@ describe TopicQuery do
     end
 
     it 'should include default regular category topics in latest list for anonymous users' do
-      SiteSetting.default_categories_regular = category.id.to_s
+      SiteSetting.default_categories_normal = category.id.to_s
       expect(TopicQuery.new.list_latest.topics.map(&:id)).to include(topic.id)
     end