CI/CD, pages job also on STEAM VM to use readily created venv

.gitlab-ci.yml

@@ -254,7 +254,7 @@ pages:
   image: python:3.11.8
   script:
     # install only packages containing the string "mkdocs" from requirements.txt
-    - grep "mkdocs" requirements.txt | xargs -n 1 pip install
+    - pip install -r requirements.txt
     - mkdocs build --clean --site-dir public
   artifacts:
     paths: