Backport !12868 into `v20-release`

What

Backports !12868 (merged) into v20-release

Why

As requested by @Killian-Delarue

How

Cherry-picking !12868 (merged) lead to some conflicts in the .yml file. The v20-release branch contains a CI configuration that is partially generated by CIAO, partially hand-written. In particular, the pipeline definitions before_merging.yml and schedule_extended_test.yml are hand-written. During cherry-picking, conflicts in those files were resolved with --ours (keeping the original version in v20-release). For each commit, I reran make -C ci and committed the result.

So in sum, for each commit C:

$ git cherry-pick C
$ git checkout --ours .gitlab/ci/pipelines/before_merging.yml .gitlab/ci/pipelines/schedule_extended_test.yml
$ make -C ci
$ git add .

(not tested, from memory).

Manually testing the MR

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR