Adds the parent group to the weighted data function.

src/nexusformat/nexus/tree.py

@@ -6395,6 +6395,7 @@ def weighted_data(self):
             raise NeXusError("No signal defined for this NXdata group")
         elif weights is None:
             raise NeXusError("No weights defined for this NXdata group")
+        result._group = self._group
         return result
 
     def prepare_smoothing(self):