fix: unpack _get_schema tuple return in _list_vector_indexes (#3275)

## Summary
- `_get_schema` returns `(schema_dict, schema_timestamp)` tuple, but
`_list_vector_indexes` was assigning the whole tuple to `schema_dict`,
causing subsequent `.get()` calls to fail.
- Fix by unpacking the tuple with `schema_dict, _ = ...`.

## Test plan
- [x] Verify `_list_vector_indexes` works correctly after the fix

---------

Signed-off-by: zhuwenxing <wenxing.zhu@zilliz.com>

Author: zhuwenxing

pymilvus/milvus_client/milvus_client.py

@@ -2346,7 +2346,7 @@ def _is_collection_loaded(self, collection_name: str, timeout: Optional[float] =
     def _list_vector_indexes(
         self, collection_name: str, timeout: Optional[float] = None, **kwargs
     ) -> List[str]:
-        schema_dict = self._get_connection()._get_schema(
+        schema_dict, _ = self._get_connection()._get_schema(
             collection_name,
             timeout=timeout,
             context=self._generate_call_context(**kwargs),

tests/test_milvus_client.py

@@ -689,6 +689,58 @@ def test_list_indexes(self):
 
             assert result == ["index1", "index2"]
 
+    def test_list_vector_indexes(self):
+        """Test _list_vector_indexes correctly unpacks _get_schema tuple return."""
+        mock_handler = MagicMock()
+        mock_handler.get_server_type.return_value = "milvus"
+
+        schema_dict = {
+            "fields": [
+                {"name": "id", "type": DataType.INT64},
+                {"name": "vector", "type": DataType.FLOAT_VECTOR},
+            ]
+        }
+        mock_handler._get_schema.return_value = (schema_dict, 12345)
+
+        mock_index = MagicMock()
+        mock_index.field_name = "vector"
+        mock_index.index_name = "vec_index"
+        mock_handler.list_indexes.return_value = [mock_index]
+        mock_handler.describe_index.return_value = {
+            "field_name": "vector",
+            "index_name": "vec_index",
+        }
+
+        with patch(
+            "pymilvus.milvus_client.milvus_client.create_connection", return_value="test"
+        ), patch("pymilvus.orm.connections.Connections._fetch_handler", return_value=mock_handler):
+            client = MilvusClient()
+            result = client._list_vector_indexes("test_collection")
+
+            assert result == ["vec_index"]
+            mock_handler._get_schema.assert_called_once()
+
+    def test_list_vector_indexes_no_vector_fields(self):
+        """Test _list_vector_indexes returns empty list when no vector fields."""
+        mock_handler = MagicMock()
+        mock_handler.get_server_type.return_value = "milvus"
+
+        schema_dict = {
+            "fields": [
+                {"name": "id", "type": DataType.INT64},
+                {"name": "text", "type": DataType.VARCHAR},
+            ]
+        }
+        mock_handler._get_schema.return_value = (schema_dict, 12345)
+
+        with patch(
+            "pymilvus.milvus_client.milvus_client.create_connection", return_value="test"
+        ), patch("pymilvus.orm.connections.Connections._fetch_handler", return_value=mock_handler):
+            client = MilvusClient()
+            result = client._list_vector_indexes("test_collection")
+
+            assert result == []
+
 
 # ============================================================
 # MilvusClient Alias Operations Tests