fix shellcheck

packaging/deb/prerm

@@ -10,7 +10,7 @@ case "$1" in
             units=$(systemctl list-units --plain --no-legend --all 'terraria@*.service' | awk '{print $1}')
             if [ -n "$units" ]; then
                 echo "Stopping Terraria instances: $units"
-                systemctl stop $units || true
+                systemctl stop "$units" || true
             fi
         fi
         ;;