How to make data stream and ignore_malformed coexist?

Question

PUT _index_template/ig-test
{
  "template": {
    "settings": {
      "index": {
        "mapping": {
          "ignore_malformed": true
        }
      }
    }
  },
  "index_patterns": [
    "ig-test*"
  ],
  "data_stream": {}
}

data stream timestamp field [@timestamp] has disallowed [ignore_malformed]

How to make every "field" support ignore_malformed?