python_install minimal script

templates/python/partial/python_install.yml

-python_install:
-    image: python:${IMAGE_TAG}
-    stage: ${ENV_SETUP}
-    variables:
-        PYTHON_SETUP: "pip install .[TESTS]"
-        IMAGE_TAG: "latest"
-        STAGE: "env_setup"
-    script:
-        - python --version  # Debug
-        - python -m venv venv --upgrade-deps || python -m venv venv  # upgrade-deps is not supported before 3.9
-        - source venv/bin/activate
-        - ${PYTHON_SETUP}
-        - pytest
-    only:
-        changes:
-            - ./**/*.py
-            - .gitlab-ci.yml
-            - pyproject.toml
+.python_install: &python_install
+  - python --version  # Debug
+  - python -m venv venv --upgrade-deps || python -m venv venv  # upgrade-deps is not supported before 3.9
+  - source venv/bin/activate
+  - ${PYTHON_SETUP}