Setting up continuous integration with django 3, postgres and gitlab CI - django

Question

I'm setting up a continuous integration with Django 3 and Gitlab CI.
Having done it previously with Django 2 but now I'm struggling to get things done with Django 3.
This warning is shown and I'm wondering if it's the reason :
/usr/local/lib/python3.8/site-packages/django/db/backends/postgresql/base.py:304: RuntimeWarning: Normally Django will use a connection to the 'postgres' database to avoid running initialization queries against the production database when it's not needed (for example, when running tests). Django was unable to create a connection to the 'postgres' database and will use the first PostgreSQL database instead.
And this error at the end :
django.db.utils.OperationalError: could not translate host name "postgres" to address: Name or service not known
Here is my config :
image: python:3.8
services:
- postgres:10.17
variables:
POSTGRES_DB : db_test
POSTGRES_USER : postgres
POSTGRES_PASSWORD : ""
POSTGRES_HOST : postgres
POSTGRES_PORT : 5432
stages:
- tests
cache:
paths:
- ~/.cache/pip/
before_script:
- python -V
- apt-get update && apt install -y -qq python3-pip
- pip install -r requirements.txt
test:
stage: tests
variables:
DATABASE_URL: "postgres://postgres:postgres#postgres:5432/$POSTGRES_DB"
script:
- coverage run manage.py test
- coverage report
coverage: "/TOTAL.+ ([0-9]{1,3}%)/"
Will be grateful if somebody can help me fix this.