Fix Dbus error when using the systemd service.

Before it commit you will get a error related to the Dbus activation because the service was trying to call it as root user but in a different session, the error is like 'Error(Dbus(D-Bus error: Server address of type unix was missing argument path or abstract (org.freedesktop.DBus.Error.BadAddress)'.

upcheck.service

@@ -1,12 +1,13 @@
 [Unit]
- Description=Automatically check updates and send notifications via libnotify
+ Description=Automatically check updates and send notifications via notify-rust
  After=network-online.target
+ ConditionUser=!root
 
 [Service]
- Type=simple
+ Type=oneshot
  ExecStart=/usr/bin/upcheck
  KillMode=process
  KillSignal=SIGINT
 
 [Install]
- WantedBy=multi-user.target
+ WantedBy=default.target

upcheck.timer

@@ -1,5 +1,5 @@
 [Unit]
- Description=Check for ArchLinux available updates every 1.5 hours.
+ Description=Check for ArchLinux available updates according to OnUnitActiveSec= time, default 1h 30min.
 
 [Timer]
  OnBootSec=10min