FIX: mark topics in sub categories as unread when dismissing parent

Previously we would only dismiss the parent category and leave the
child categories unread

spec/requests/topics_controller_spec.rb

@@ -2039,6 +2039,27 @@ RSpec.describe TopicsController do
         expect(response.status).to eq(400)
       end
 
+      it "can mark sub-categories unread" do
+        # TODO do we want to skip category definition by default in fabricator
+        category = Fabricate(:category, skip_category_definition: true)
+        sub = Fabricate(:category, parent_category_id: category.id, skip_category_definition: true)
+
+        topic.update!(category_id: sub.id)
+
+        post1 = create_post(user: user, topic_id: topic.id)
+        create_post(topic_id: topic.id)
+
+        put "/topics/bulk.json", params: {
+          category_id: category.id,
+          include_subcategories: true,
+          filter: 'unread',
+          operation: { type: 'dismiss_posts' }
+        }
+
+        expect(response.status).to eq(200)
+        expect(TopicUser.get(post1.topic, post1.user).last_read_post_number).to eq(2)
+      end
+
       it "can find unread" do
         # mark all unread muted
         put "/topics/bulk.json", params: {