[MM-61094] Fix errcheck issues in server/channels/app/app_test.go (#29124)

server/.golangci.yml

@@ -84,7 +84,6 @@ issues:
         channels/api4/team_test.go|\
         channels/api4/user_test.go|\
         channels/api4/websocket_test.go|\
-        channels/app/app_test.go|\
         channels/app/auto_responder_test.go|\
         channels/app/bot_test.go|\
         channels/app/brand.go|\