Merge branch 'renovate/docker-python-3.x' into 'master'

Update python Docker tag to v3.9

See merge request !2

.gitlab-ci.yml

 test:
-  image: python:3.8-buster
+  image: python:3.9-buster
   before_script:
     - apt-get update -y -qq && apt-get install -y -qq yarnpkg
     - pip install -q Django