Update .gitlab-ci.yml

.gitlab-ci.yml

@@ -23,6 +23,8 @@ cache:
     - .cache/pip
     - venv/
 
+preparation:
+  tag: docker
   before_script:
     - python --version  # For debugging
     - pip install virtualenv
@@ -30,6 +32,7 @@ before_script:
     - source venv/bin/activate
 
 test:
+  tag: docker
   script:
     - python setup.py test
     - pip install tox flake8  # you can also use tox