FIX: Update topic route id param (#16166)

This update topic route has never worked. Better late than never. I am
in favor of using non-slug urls when using the api so I do think we
should fix this route.

Just thought I would update the `:id` param to `:topic_id` here in the
routes file instead of updating the controller to handle both params.

Added a spec to test this route.

Also added the same constraint we have on other topic routes to ensure
we only pass in an ID that is a digit.

config/routes.rb

@@ -767,7 +767,7 @@ Discourse::Application.routes.draw do
 
     # Topics resource
     get "t/:id" => "topics#show"
-    put "t/:id" => "topics#update"
+    put "t/:topic_id" => "topics#update", constraints: { topic_id: /\d+/ }
     delete "t/:id" => "topics#destroy"
     put "t/:id/archive-message" => "topics#archive_message"
     put "t/:id/move-to-inbox" => "topics#move_to_inbox"

spec/requests/topics_controller_spec.rb

@@ -1317,6 +1317,27 @@ RSpec.describe TopicsController do
           expect(payload["title"]).to eq('This is a new title for the topic')
         end
 
+        it 'allows update on short non-slug url' do
+          put "/t/#{topic.id}.json", params: {
+            title: 'This is a new title for the topic'
+          }
+
+          topic.reload
+          expect(topic.title).to eq('This is a new title for the topic')
+        end
+
+        it 'only allows update on digit ids' do
+          non_digit_id = "asdf"
+          original_title = topic.title
+          put "/t/#{non_digit_id}.json", params: {
+            title: 'This is a new title for the topic'
+          }
+
+          topic.reload
+          expect(topic.title).to eq(original_title)
+          expect(response.status).to eq(404)
+        end
+
         it 'allows a change of then updating the OP' do
           topic.update(user: user)
           topic.first_post.update(user: user)