Oder so?

.gitlab-ci.yml

 image: python:latest
 
 before_script:
-  - pip install poetry
-  - pip install numpy
-  - pip install coverage
+  - curl -sSL https://install.python-poetry.org | python3 -
+  - export PATH="$PATH:$HOME/.poetry/bin/" 
+  - source $HOME/.poetry/env 
 
 stages:
   - build_package