DEV: Update bench.rb for core changes (#8670)

- Use new api key rake task
- Switch to header-based API auth
- Stop hard-coding topic id

script/profile_db_generator.rb

@@ -65,7 +65,7 @@ unless Rails.env == "profile"
 end
 
 def ensure_perf_test_topic_has_right_title!
-  t = Topic.find(179)
+  t = Topic.where(archetype: :regular).last
   t.title = "I am a topic used for perf tests"
   t.save! if t.title_changed?
 end