NotificationStack: Check if notification was already shown

data/gala.metainfo.xml.in

@@ -25,14 +25,15 @@
   <update_contact>contact_at_elementary.io</update_contact>
 
   <releases>
-    <release version="7.1.3" date="2023-09-13" urgency="medium">
+    <release version="7.1.3" date="2023-09-29" urgency="medium">
       <description>
         <p>Improvements:</p>
         <ul>
           <li>Updated translations</li>
         </ul>
       </description>
       <issues>
+        <issue url="https://github.com/elementary/notifications/issues/218">Notifications appear in the middle of the screen</issue>
         <issue url="https://github.com/elementary/gala/issues/1774">Scheduled switch to dark style does not dim the wallpaper after cold reboot on elementary OS 7.1</issue>
         <issue url="https://github.com/elementary/gala/issues/1261">Alt + Shift unnecessarily blocked when there is only one keyboard layout</issue>
       </issues>

src/NotificationStack.vala

@@ -48,7 +48,7 @@ public class Gala.NotificationStack : Object {
         update_stack_allocation ();
     }
 
-    public void show_notification (Meta.WindowActor notification, bool animate) {
+    public void show_notification (Meta.WindowActor notification, bool animate) requires (!notifications.contains (notification)) {
         notification.set_pivot_point (0.5f, 0.5f);
 
         unowned Meta.Window window = notification.get_meta_window ();