Collect coverage data for the default branch from FOSS

Everyone can contribute. Help move this issue forward while earning points, leveling up and collecting rewards.

• Close this issue

We essentially stopped running as-if-foss pipelines after !142899 (merged)

This means the default branch coverage data will not contain FOSS coverage. This can be an issue because we have lines which can only be reached under FOSS mode. We'll never be able to cover those cases if we don't also collect coverage data from FOSS.

We can possibly make the default branch pipeline collect whatever the latest default branch FOSS pipeline. It'll look like this:

needs:
  - project: gitlab-org/gitlab-foss
    ref: ${CI_COMMIT_REF_NAME}
    job: rspec:artifact-collector unit
  - project: gitlab-org/gitlab-foss
    ref: ${CI_COMMIT_REF_NAME}
    job: rspec:artifact-collector system
  - project: gitlab-org/gitlab-foss
    ref: ${CI_COMMIT_REF_NAME}
    job: rspec:artifact-collector remainder

This likely cannot fetch the up-to-date coverage data from FOSS (because we're not waiting for the corresponding FOSS pipeline to finish, and it can fetch artifacts from older pipelines), but it might be close enough.

More context can be found at !142899 (comment 1750833773)