The stdout progress feed from `git gc` is fairly verbose and
targeted at audiences running it interactively. Since our cron for
this iterates over thoudands of repositories on our Gitea servers,
we don't need to send the progress info to all our sysadmins by
E-mail. Instead use the --quiet option to the gc subcommand so that
progress output will be suppressed.
If this still proves too verbose (as in, continues to result in
E-mail to root even when there are no failures), we can try
redirecting stdout to /dev/null.
Change-Id: Idc06e48cbf85e127a343c2a3cf51a35e6ed09685
d0ff3e48d1