browser_output is empty when testing with Drupal 11 and _phpunit_concurrent=0

Migrated issue

Reported by: chi

Related to !272 (merged)

The browser_output folder in artifacts is empty when testing on D11.

Job reference
https://git.drupalcode.org/project/double_field/-/pipelines/310217

That works well on Drupal 10 jobs.

Originally raised on Slack
https://drupal.slack.com/archives/CGKLP028K/p1728990199138709

This issue only affects phpunit jobs running with Drupal 11. It does not affect Drupal 10 or Drupal 7 phpunit jobs.

Interim fix

If your pipeline is using _PHPUNIT_CONCURENT: 0 and you need to fix this temporarily, before gitlab_templates makes a new release, you can add the following into your project's .gitlab-ci.yml

variables:
  _PHPUNIT_EXTRA: "-c $CI_PROJECT_DIR/$_WEB_ROOT/core"

Tasks

1. if the project does not have phpunit.xml then reference it via -c  argument [done]
2. do not add this if already specified in _PHPUNIT_EXTRA [done]
3. do the same in test-only.sh [done]