Subprojects on GitLab are not supported

[PerchunPak]

For example, https://gitlab.com/gitlab-org/editor-extensions/gitlab.vim crashes with

❯ , nurl https://gitlab.com/gitlab-org/editor-extensions/gitlab.vim
$ nix flake prefetch --extra-experimental-features 'nix-command flakes' --json gitlab:gitlab-org%2Feditor-extensions/gitlab.vim/74a845366a7edf6b400ab9a4d2ec83bacadea930
error:
       … while fetching the input 'gitlab:gitlab-org/editor-extensions/gitlab.vim/74a845366a7edf6b400ab9a4d2ec83bacadea930'

       error: unable to download 'https://gitlab.com/api/v4/projects/gitlab-org%2Feditor-extensions/repository/commits?ref_name=gitlab.vim/74a845366a7edf6b400ab9a4d2ec83bacadea930': HTTP error 404

       response body:

       {"message":"404 Project Not Found"}
Error: command exited with exit status: 1

But curl https://gitlab.com/api/v4/projects/gitlab-org%2Feditor-extensions%2Fgitlab.vim/repository/commits?ref_name=74a845366a7edf6b400ab9a4d2ec83bacadea930 works (gitlab.vim got moved from repository path to ref).