lintian: the child pipeline lintian-errors is always triggered on the default branch instead of the same branch as the parent job

Background

When a pipeline ci-package-builder is triggered on a non-default branch of pkg/lintian, its local-post-binary-build-gitlab-ci.yml defines a child pipeline lintian-errors which triggers a pipeline in tests/lintian-errors on the default branch instead of the reusing the same branch as the parent job. This results in an issue in the job lintian-errors-test since the fake package lintian-errors is not built in the right apertis release. This bug has always been there, but has been highlighted by the rebase on bookworm and because we moved the definition of the testing jobs into the package instead of being defined in ci-package-builder.

Reproducibility

How often the issue is hit when repeating the steps to reproduce and changing nothing?

Put the ✅ in the most appropriate entry:

1. ✅ always
2. often, but not always
3. rarely

Impact of bug

This makes impossible to test the lintian apertis profile a previous apertis release, but it works in the current dev release. This is a low severity bug since we rarely update the apertis lintian profile and we can anyway test it in the current release. But, it's quite annoying after a rebase since we cannot test a backport of our apertis lintian profile.

For instance the pipeline in pkg/lintian!38 fails due to this issue.

Outcomes

TBD

Management data

This section is for management only, it should be the last one in the description.

/cc @andrunko @em @Balasubramanian @sudarshan @wlozano

Phabricator link: https://phabricator.apertis.org/T10536