Update .gitlab-ci.yml

.gitlab-ci.yml

 image: alpine
 
+before_script:
+  - apt-get update -qq && apt-get install -y -qq python3, python3-pip
 pages:
   script:
-  - apk add python3, python3-pkgconfig, python3-pip
-  - pip install sphinx, pytest
+  - pip install sphinx
   artifacts:
     paths:
     - public