I just tried to push a commit to the cmucl repo and got an error from cmucl's post-receive-hook.

I think it's complaining that /project/cmucl/trac/log/trac.log has the wrong permissions.  All of the backup logs are owned www-data.cmucl. But the current log is www-data.www-data.  The actual permissions (rw-rw-r--) on the file seems to be ok, compared to the others.