change sudoers file mode to 440 to match recommended defaults.
From the sudoers man page.
> the default file mode is 0440 (read‐able by owner and group, writable
by none).
> The default mode may be changed via the “sudoers_mode” option to the
sudoers
> Plugin line in the sudo.conf(5) file.
Fixes: https://tracker.ceph.com/issues/48169
Signed-off-by: David Turner <drakonstein@gmail.com>