php 8.3 compat

src/PropertyBag.php

@@ -75,7 +75,7 @@ class PropertyBag implements \IteratorAggregate
         return $this;
     }
 
-    public function getIterator()
+    public function getIterator(): \Traversable
     {
         return new \ArrayObject($this->elements + $this->xprops);
     }