gitlab-ci.yml: fix pipeline for ubuntu:latest (noble)

Since we are using ubuntu:latest, and noble was released, some tests are failing.

shellcheck needs python3 to run, which was possibly installed by default in previous ubuntu images and is no longer the case.

Ignore dist-packages python files during our coverage tests.

Fixes: #388 (closed)

Signed-off-by: Georgia Garcia georgia.garcia@canonical.com