Improve Transmogrifier.upgrade_user_from_ap_id/2

• Use User.update_and_set_cache/1 instead of Repo.update/2 (disscussion)
• Use PleromaJobQue instead of Task to run user_upgrade_task/1
• Remove :timer.sleep(1000) from the corresponding test (PleromaJobQue executes jobs in tests synchronously)