Backport !6159 to v15-release

Context

Backport !6159 (merged) to v15-release.

This MR is not directly needed, but it is a prerequisite of !6803 (merged) which we do want.

Manually testing the MR

I ran the following on my backport of !6803 (merged) to check the set of released packages:

./scripts/opam-release.sh 15.0 https://gitlab.com/tezos/tezos/-/package_files/58329735/download

It does differ from what we released for Octez 15.0 but after looking into it it was actually due to the fact that the early version of !6803 (merged) I made for Octez 15.0 worked a bit differently in how it did the transitive closure: it did the transitive closure of dune targets instead of opam packages.

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