chore: update langchain 1.2.0 (#19991)

* chore: update langchain 1.2.0

* chore: format

backend/open_webui/routers/retrieval.py

@@ -28,8 +28,11 @@ from pydantic import BaseModel
 import tiktoken
 
 
-from langchain.text_splitter import RecursiveCharacterTextSplitter, TokenTextSplitter
-from langchain_text_splitters import MarkdownHeaderTextSplitter
+from langchain_text_splitters import (
+    RecursiveCharacterTextSplitter,
+    TokenTextSplitter,
+    MarkdownHeaderTextSplitter,
+)
 from langchain_core.documents import Document
 
 from open_webui.models.files import FileModel, FileUpdateForm, Files