Fix deployment to GitLab Pages

Deplyoment to GitLab Pages did not yet take the subpath into account.
Now fixed by using the commandline option `--base-url`.
2 jobs for 19-current-configuration-does-not-work-on-subpath in 5 minutes and 6 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #63382
run_jekyll_latest_dependencies

00:05:03

passed #63383
run_jekyll_production

00:05:06