[CI] Adjust to zola

.gitlab-ci.yml

-image: python:3.9-bullseye
+image: alpine:latest
 
 variables:
   GIT_SUBMODULE_STRATEGY: recursive
-  PIP_EXTRA_INDEX_URL: https://edugit.org/api/v4/projects/257/packages/pypi/simple
 
 pages:
   stage: deploy
   before_script:
-  - apt-get -y update && apt-get -y install po4a
-  - pip install -r requirements.txt
+  - apk add --update-cache --repository http://dl-cdn.alpinelinux.org/alpine/edge/community/ zola
+  - apk add yarn
+  - yarn install
   script:
-  - make publish; make publish
-  - cp _redirects public/
+  - zola build
   artifacts:
     paths:
     - public/