force `subprocess.run` to check return code is 0

In general, this should help to capture unintentional errors.

Where the change has created failures, they have been fixed. (Mostly because the git repository that was looked for was missing.)

.gitlab-ci.yml

@@ -15,7 +15,7 @@ stages:
   - ls -l
   - pip install -U pip
   - pip --version
-  - pip install pytest black ruff
+  - pip install pytest black ruff pydocstyle
   - pytest --version
   - cat /etc/issue
 
@@ -79,6 +79,9 @@ style:
     - ruff --version
     - ruff .
     - black --check --diff .
+    - pydocstyle mpsd-software-environment.py
+    - pydocstyle tests.py
+    # we could also use `ruff --select D` for pycodestyle. But the behaviour is not exactly the same.
 
 
 test-bullseye: