chore: update langchain 1.2.0 (#19991)

* chore: update langchain 1.2.0

* chore: format

backend/open_webui/retrieval/utils.py

@@ -12,7 +12,10 @@ import re
 
 from urllib.parse import quote
 from huggingface_hub import snapshot_download
-from langchain.retrievers import ContextualCompressionRetriever, EnsembleRetriever
+from langchain_classic.retrievers import (
+    ContextualCompressionRetriever,
+    EnsembleRetriever,
+)
 from langchain_community.retrievers import BM25Retriever
 from langchain_core.documents import Document