[MM-61100] Fix errcheck issues in server/channels/app/busy_test.go (#28786)

server/.golangci.yml

@@ -87,7 +87,6 @@ issues:
         channels/app/auto_responder_test.go|\
         channels/app/bot_test.go|\
         channels/app/brand.go|\
-        channels/app/busy_test.go|\
         channels/app/channel.go|\
         channels/app/channel_bookmark_test.go|\
         channels/app/channel_test.go|\