man/soft-reboot: order surviving services before shutdown.target

Prompted by #32895

Rather than ordering with each power operation targets,
ordering against shutdown.target which is a valid
synchronization point. This has no effect if soft-reboot
is being performed.

man/systemd-soft-reboot.service.xml

@@ -115,7 +115,7 @@ IgnoreOnIsolate=yes
 DefaultDependencies=no
 After=basic.target
 Conflicts=reboot.target kexec.target poweroff.target halt.target rescue.target emergency.target
-Before=reboot.target kexec.target poweroff.target halt.target rescue.target emergency.target
+Before=shutdown.target rescue.target emergency.target
 
 [Service]
 Type=oneshot