fix(milvus): Fix milvus store search with topk always set to 4 (#2131)

dbgpt/storage/vector_store/milvus_store.py

@@ -458,7 +458,7 @@ def similar_search_with_scores(
         # convert to milvus expr filter.
         milvus_filter_expr = self.convert_metadata_filters(filters) if filters else None
         _, docs_and_scores = self._search(
-            query=text, topk=topk, expr=milvus_filter_expr
+            query=text, k=topk, expr=milvus_filter_expr
         )
         if any(score < 0.0 or score > 1.0 for _, score, id in docs_and_scores):
             logger.warning(