FEATURE: Allow TL4 users to see unlisted topics (#19890)

TL4 users can already list and unlist topics, but they can't see
the unlisted topics. This change brings this to par by allowing
TL4 users to also see unlisted topics.

lib/guardian/topic_guardian.rb

@@ -277,6 +277,10 @@ module TopicGuardian
       )
   end
 
+  def can_see_unlisted_topics?
+    is_staff? || @user.has_trust_level?(TrustLevel[4])
+  end
+
   def can_get_access_to_topic?(topic)
     topic&.access_topic_via_group.present? && authenticated?
   end