ci: switch to v2 version of CI

.gitlab-ci.yml

@@ -4,5 +4,5 @@
 
 include:
   - project: "open-source/gitlab-ci-templates"
-    ref: "branch/default"
+    ref: "branch/v2"
     file:
@@ -8,4 +8,5 @@
     file:
+      - "templates/base.yml"  # mandatory base template
       - "templates/no-duplicated-ci-pipelines.yml"  # use workflow to avoid duplicated pipelines
       - "templates/lint/flake8.yml"  # will do the equivalent of 'tox -e flake8'
       - "templates/lint/black.yml"  # will do the equivalent of 'tox -e black'