PanelSpy - fix error handling methods that have a return value

E.g. `ReferenceUI` has `self.get_object_name(context)` - since value wasn't returned, it was returning `None`, breaking the tests.

src/bonsai/test/bim/test_feature.py

@@ -170,7 +170,7 @@ class PanelSpy:
             panel = None if default_closed else self
             return header, panel
         else:
-            getattr(self.blender_panel, self.spied_attr)(self, *args, **kwargs)
+            return getattr(self.blender_panel, self.spied_attr)(self, *args, **kwargs)
 
 
 class OperatorSpy: