`env-set` does not properly display the error message when setting a reserved variable

[EtienneM]

 scalingo --app biniou env-set PORT=12345                                                                              
 !     400 Bad Request → 

But the body response is correctly sent:

{"failed":[{"id":"REDACTED","app_id":"REDACTED","name":"PORT","value":"12345","errors":{"name":["is reserved"]}}]}

[EtienneM]

The error returned by the API is a 400 with a weird body:

{
  "failed": [
    {
      "id": "REDACTED",
      "app_id": "REDACTED",
      "name": "PORT",
      "value": "1234",
      "errors": {
        "name": [
          "is reserved"
        ]
      }
    }
  ]
}

[EtienneM]

Production deployment:

https://github.com/Scalingo/dashboard-next/pull/2656
https://github.com/Scalingo/api/pull/3177