[GitLab CI] Improve failure reporting summary

Looks like https://docs.gitlab.com/ee/ci/testing/unit_test_reports.html

OK so there is a summary here, but it is a couple of clicks to find, and the failure details are in a modal:

https://git.drupalcode.org/project/drupal/-/pipelines/25513/test_report

This is also tedious on contrib testing too. Sometime even the 'tests' tab does not have the error. For example, this 'tests' tab /scheduler_content_moderation_integration/-/pipelines/25812/test_report - there is no phpunit job row in the table. But from the pipeline overview you can see that the phpunit job ran and failed.

Reading https://docs.gitlab.com/ee/ci/testing/unit_test_reports.html a bit more properly it's what we're already doing (for core at least) so is not helpful particularly for what I'm thinking of here.

Thanks for creating this issue @catch, and the tip about Ctrl+F'ing until the actual error pops up, it was very helpful.

> the tip about Ctrl+F'ing until the actual error pops up, it was very helpful.

Sort of -- if you know what a failure looks like in the output of the particular test runner. I was recently working on a MR which added JS and I had no idea what string to search for in the test output.

It would still be great, if the reason why a test is failing, could be made clearer for the user :)