ci(gitlab-ci): use templates from a common repository

.gitlab-ci.yml

@@ -3,6 +3,7 @@ default:
   image: python:3.7
 
 include:
+  - ".gitlab-ci-extended.yml"
   - project: "open-source/gitlab-ci-templates"
     ref: "branch/default"
     file:
@@ -13,7 +14,6 @@ include:
       - "templates/tests/py3.yml"  # will do the equivalent of 'tox -e py3'
       - "templates/create-release-on-heptapod.yml"  # this will create a release on heptapod
       - "templates/upload-to-pypi.yml"  # on a new mercurial tag (expected to be done with release-new), will push a release on pypi
-  - '.gitlab-ci-extended.yml'
 
 stages:
   - lint