units: add dep on systemd-logind.service by user@.service

Let's make sure logind is accessible by the time user@.service runs, and
that logind stays around as long as it does so.

Addresses an issue reported here:

https://lists.freedesktop.org/archives/systemd-devel/2024-June/050468.html

This addresses an issued introduced by
278e815bfa, which dropped the a dependency
from user@.service systemd-user-sessions.service without replacement.
While dropping that dependency does make sense, it should have been
replaced with the weaker dependency on systemd-logind.service, hence fix
that now.

user@.service is after all a logind concept, hence logind really should
be around for its lifetime.

systemd-user-sessions.service is a later milestone that only really
should apply to regular users (not root), hence it's too strong a
requirement.

units/user-runtime-dir@.service.in

@@ -10,7 +10,7 @@
 [Unit]
 Description=User Runtime Directory /run/user/%i
 Documentation=man:user@.service(5)
-After=dbus.service
+After=systemd-logind.service dbus.service
 IgnoreOnIsolate=yes
 
 [Service]

units/user@.service.in

@@ -11,7 +11,7 @@
 Description=User Manager for UID %i
 Documentation=man:user@.service(5)
 BindsTo=user-runtime-dir@%i.service
-After=user-runtime-dir@%i.service dbus.service systemd-oomd.service
+After=systemd-logind.service user-runtime-dir@%i.service dbus.service systemd-oomd.service
 IgnoreOnIsolate=yes
 
 [Service]