ifcopenshell.util.element.get_type to be less strict again after d443c5e

I guess by accident in d443c5e I've made this method too strict and it broke get_references using it for IfcPropertySets. Maybe it's a good idea to make it more strict in the future, for now just restoring the previous behaviour.

src/ifcopenshell-python/ifcopenshell/util/classification.py

@@ -27,7 +27,7 @@ def get_references(element: ifcopenshell.entity_instance, should_inherit=True) -
             references := getattr(element, "HasExternalReference", None)
         ) is not None:
             return {r.RelatingReference for r in references}
-    if should_inherit:
+    if should_inherit and element.is_a("IfcObject"):
         element_type = ifcopenshell.util.element.get_type(element)
         if element_type and element_type != element:
             results = get_references(element_type)