systemctl: do not shutdown immediately on scheduled shutdown

systemctl: do not shutdown immediately on scheduled shutdown

When, for whatever reason, a scheduled shutdown fails to be set, systemd
will proceed with immediate shutdown without allowing the user to react.
This is counterintuitive because when a scheduled shutdown is issued,
it means the user wants to shutdown at a specified time in the future,
not immediately. This patch prevents the immediate shutdown and informs
the user that no action will be taken.

Fixes: #17575
Gbp-Pq: Topic debian
Gbp-Pq: Name systemctl-do-not-shutdown-immediately-on-scheduled-shutdo.patch