Fixed errcheck issues in server/channels/app/onboarding_test.go (#29066)

server/.golangci.yml

@@ -107,7 +107,6 @@ issues:
         channels/app/job_test.go|\
         channels/app/login_test.go|\
         channels/app/migrations.go|\
-        channels/app/onboarding_test.go|\
         channels/app/permissions.go|\
         channels/app/permissions_test.go|\
         channels/app/platform/busy_test.go|\