Improve visibility of error from expand-composer.php script

Yes we can improve the visibility of those messages, both in the .php script and the template.

Tested in the d9-basic downstream branch.
https://git.drupalcode.org/project/gitlab_templates_downstream/-/jobs/54...
Ready for review

That's great, I think the output now is much clearer and we can spot the error easier than before.

RTBC but we need to revert the change in ".gitlab-ci.yml". I'll set it as NW but once that's done, it can go directly to RTBC.

Thanks. I've removed the test variable.

Merged. Thanks!