This might not be the same cause or solution as git test receive wrapper fails so filing it separately.

Anon git push is broken again

remote: error: cannot lock ref 'HEAD': Unable to create '/home/b-ikiwiki/source.git/./HEAD.lock': Permission denied
To git://git.ikiwiki.info/
 ! [remote rejected]     master -> master (failed to update ref)

Jon, 2020-10-06