Trying to access Postgres service from docker image

[orkenstein]

I'm trying to connect to Postgres db from within my Docker image to run tests:

  test_backend:
    runs-on:
      group: ubuntu-large
    needs: build_backend

    # Service containers to run with `container-job`
    services:
      # Label used to access the service container
      postgres:
        # Docker Hub image
        image: postgres
        # Provide the password for postgres
        env:
          POSTGRES_PASSWORD: postgres
        # Set health checks to wait until postgres has started
        options: >-
          --health-cmd pg_isready
          --health-interval 10s
          --health-timeout 5s
          --health-retries 5
        ports:
          # Maps tcp port 5432 on service container to the host
          - 5432:5432

    steps:
    - name: Run tests in container
      uses: addnab/docker-run-action@v3
      with:
        image: backend-py:${{github.sha}}
        run: ./manage.py test --noinput
        options: --env-file .github/workflows/env.test

There is a script, that tries to connect to Postgres running as a service. However I can't figure out, how to set the correct network/host value. I've tried to set in env.test:

DATABASE_URL=postgres://${POSTGRES_USER}:${POSTGRES_PASSWORD}@${INPUT_DOCKER_NETWORK}:5432/${POSTGRES_DB}

Which gives me error:

django.db.utils.OperationalError: could not translate host name "${input_docker_network}" to address: Name or service not known

How should I specify the host name to successfully connect to Postgres GitHub service?