Update .gitlab-ci.yml

.gitlab-ci.yml

 test_job:
     stage: test
     tags:
-        - intro-shell
+        - intro-docker
     script:
-        - python3 -m venv venv
-        - source ./venv/bin/activate
-        - python3 -m pip install -r requirements.txt
-        - python3 -m unittest tests/coords_test.py
+        - pip install -r requirements.txt
+        - python -m unittest tests/coords_test.py