fix: Notification model getUpdatedAt method uses created_at date …

…instead of `updated_at` (#2417)

Co-authored-by: Peter Ojo <peterojo@users.noreply.github.com>

Model/Notification.php

@@ -272,7 +272,7 @@ public function setCreatedAt(DateTime $createdAt): NotificationInterface
 
     public function getUpdatedAt(): ?string
     {
-        $updatedAt = $this->getData(self::CREATED_AT);
+        $updatedAt = $this->getData(self::UPDATED_AT);
 
         if ($updatedAt instanceOf Datetime) {
             return $updatedAt->format('Y-m-d H:i:s');