head-node: ‘unattended-upgrade’ restarts itself.

* head-node.scm <top level>(unattended-upgrade-configuration): Add
‘unattended-upgrade’ to the list of services to restart.

head-node.scm

@@ -481,7 +481,7 @@ CALENDAR, a gexp, and ensures at least FREE-SPACE GiB are available."
                           (unattended-upgrade-configuration
                            (operating-system-file this-file)
                            (services-to-restart
-                            '(mcron nginx guix-daemon qemu-binfmt tor))
+                            '(mcron nginx guix-daemon qemu-binfmt tor unattended-upgrade))
                            (channels
                             #~(cons* (channel
                                       (name 'cuirass)