`tar_git` service fails when repo to clone was once private

[Olf0]

This issue was incorrectly filed at the main repository of SailfishOS:Chum: sailfishos-chum/main#23

Quoted copy&paste from there:

I am getting the error message from a service run of tar_git:

Files could not be expanded: service error: ERROR: couldn't clone reponame

service tar_git failed:
Handling reponame
fatal: not a git repository (or any parent up to mount point /)
Stopping at filesystem boundary (GIT_DISCOVERY_ACROSS_FILESYSTEM not set).
fatal: repository '/data/service/tar_git/https___gitlab.com_nephros/reponame' does not exist
ERROR: couldn't clone reponame

Steps to reproduce:

1. on GitLAB, create a new repo

2. when creating, make sure to create a 'private' visibility

3. commit some files that should wor with tar_git service

4. create a new package at OBS

5. create a service file pulling from the above repo

6. observe the cloning error as expected

7. on Gitlab project settings, change visibility from private to public

8. trigger the service again

9. service cannot clone still

10. use any other tool to clone that repo, confirm that it works normally.