Register PlayerRegistered handler to properly set registered_slots.

Author: dysk

notifications/spec/spec_helper.rb

@@ -19,6 +19,10 @@ def event_store
             ->(event) { Notifications::SlackNotifier.new(logger: Rails.logger, event_store: client).call(event) },
             to:  [Game::NewTurnStarted, Game::PlayerDisconnected, Game::TimerReset]
           )
+          client.subscribe(
+            ->(event) { ReadModel::GameReadModelUpdater.new(logger: Rails.logger).call(event) },
+            to: [Game::PlayerRegistered]
+          )
         end
   end
 end