fix: correct [AttributeError: 'set' object has no attribute 'nodes' T… (#6699)

### Related Issue: 
https://github.com/infiniflow/ragflow/issues/6653 

### Environment:
Using nightly version [ece5903]

Elasticsearch database

Thanks for the review! My fault! I realize my initial testing wasn't
passed.

In graphrag/entity_resolution.py 
 `sub_connect_graph` is a set like` {'HELLO', 'Hi', 'How are you'}`, 
Neither accessing `.nodes` nor `.nodes()` will work, **it still causes
`AttributeError: 'set' object has no attribute 'nodes'`**

In graphrag/general/extractor.py  
The `list.extend() `method performs an in-place operation, directly
modifying the original list and returning ‘None’ rather than the
modified list.
Neither accessing
`sorted(set(node0_attrs[attr].extend(node1_attrs.get(attr, []))))` nor
`sorted(set(node0_attrs[attr].extend(node1_attrs[attr])))` will work,
**it still causes `TypeError: 'NoneType' object is not iterable`**
### Type of change

- [ ] Bug Fix AttributeError: graphrag/entity_resolution.py 
- [ ] Bug Fix TypeError: graphrag/general/extractor.py

graphrag/entity_resolution.py

@@ -111,7 +111,7 @@ class EntityResolution(Extractor):
         connect_graph.add_edges_from(resolution_result)
         async with trio.open_nursery() as nursery:
             for sub_connect_graph in nx.connected_components(connect_graph):
-                merging_nodes = list(sub_connect_graph.nodes())
+                merging_nodes = list(sub_connect_graph)
                 nursery.start_soon(lambda: self._merge_graph_nodes(graph, merging_nodes, change))
 
         # Update pagerank