Heroku run PHP artisan migrate 出错? sql [22023]

为什么会提示出现字符集错误 难道不是utf8mb4? 这是什么原因

  SQLSTATE[22023]: Invalid parameter value: 7 ERROR:  invalid value for param
  eter "client_encoding": "utf8mb4" (SQL: select * from information_schema.ta
  bles where table_schema = public and table_name = migrations and table_type
   = 'BASE TABLE')  
  SQLSTATE[22023]: Invalid parameter value: 7 ERROR:  invalid value for param
  eter "client_encoding": "utf8mb4"