Correctly link output of CSS linting (stylelint) on GitLab

Problem/Motivation

Follow-up from #3467309: Replace abandoned, not working with latest stylelint, leon0399/stylelint-formatter-gitlab with gitlab-formatters/stylelint-formatter-gitlab

I think the output could be improved - we should fix up the paths so the link in https://git.drupalcode.org/issue/drupal-3487817/-/pipelines/340184/codeq... is clickable - but that can happen in a followup.

@longwave in #3467309-19

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet