build: 固定 langchain 和 langchain-core 的版本号

requirements.txt

@@ -1,6 +1,6 @@
 langgraph>=0.2.46
-langchain>=0.3.0,<1.0.0
-langchain-core>=0.3.0,<1.0.0
+langchain==0.3.27
+langchain-core==0.3.80
 langchain-openai>=0.2.0
 langchain-google-genai>=2.0.0
 google-genai>=0.2.0