bug#74583: ‘guix git authenticate’ pre-push hook unsuitable in some cases

[Ludovic Courtès]

And when deleting a branch:

--8<---------------cut here---------------start------------->8---
guix git: .[1;31merror: .[0mGit error: odb: cannot read object: null OID cannot 
exist
error: failed to push some refs to 'codeberg.org:civodul/guix-science.git'
--8<---------------cut here---------------end--------------->8---