DEV: track the correct channel in specs

These tests are erratically failing due to distributed cache messages that
can land between tests

Ensure we are only looking for the correct messages

plugins/poll/spec/lib/polls_updater_spec.rb

@@ -54,7 +54,7 @@ describe DiscoursePoll::PollsUpdater do
   describe "update" do
 
     it "does nothing when there are no changes" do
-      message = MessageBus.track_publish do
+      message = MessageBus.track_publish("/polls/#{post.topic_id}") do
         update(post, polls)
       end.first
 
@@ -109,7 +109,7 @@ describe DiscoursePoll::PollsUpdater do
 
         expect(Poll.find_by(post: post)).to_not be
 
-        message = MessageBus.track_publish do
+        message = MessageBus.track_publish("/polls/#{post.topic_id}") do
           update(post, polls)
         end.first
 
@@ -135,7 +135,7 @@ describe DiscoursePoll::PollsUpdater do
 
           freeze_time 1.month.from_now
 
-          message = MessageBus.track_publish do
+          message = MessageBus.track_publish("/polls/#{post.topic_id}") do
             update(post, polls_with_some_attributes)
           end.first
 
@@ -166,7 +166,7 @@ describe DiscoursePoll::PollsUpdater do
         describe "inside the edit window" do
 
           it "and deletes the votes" do
-            message = MessageBus.track_publish do
+            message = MessageBus.track_publish("/polls/#{post.topic_id}") do
               update(post, polls_with_some_attributes)
             end.first