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*