How to pass HEROKU_APP_NAME from Review App to CI application

Question

I try to run test collection via newman for my Review App on CI App but I don't know how to pass URL of the app. In app.json I have something like that:

"environments": {
    "test": {
      "scripts": {
        "test-setup": "npm install -g newman",
        "test": "newman run ./src/test/collection.json -e ./src/test/environment.json --env-var \"baseUrl=$HEROKU_APP_NAME\""
      }
    }
  }

This doesn't work because HEROKU_APP_NAME is not passed to the CI application.

I bet I missed something obvious, but I spent a few hours reading Heroku docs and didn't find anything useful.

Tried to prepare postdeploy script without success.