The previous URL pattern is 404 with current gitlab, this is working today probably because it is in shacache.
Updating the download URL to the new URL pattern produces a tarball with a different checksum. Unlike github and unlike my assumptions, gitlab does not guarantee hash stability for archives ( https://gitlab.com/gitlab-org/gitlab/-/issues/402616#note_1330840501 )
To keep the exact same file, I downloaded it from shacache and uploaded it in a gitlab registry release, following https://lab.nexedi.com/help/user/packages/generic_packages/index.md
At the same time, the repository was moved from bk namespace to nexedi namespace