add missing canPurgeItem for CommonDBChild

Author: cconard96

src/CommonDBChild.php

@@ -169,6 +169,11 @@ public function canDeleteItem(): bool
         return $this->canChildItem('canUpdateItem', 'canUpdate');
     }
 
+    public function canPurgeItem(): bool
+    {
+        return $this->canChildItem('canUpdateItem', 'canUpdate');
+    }
+
 
     /**
      * @since 0.84