fix moved imports for langchain 0.4

fiscal.py

@@ -1,13 +1,18 @@
 import os
 from typing import Dict
+
 from langchain_huggingface import HuggingFaceEmbeddings, ChatHuggingFace, HuggingFaceEndpoint
 from langchain_community.vectorstores import Chroma
 from langchain_community.retrievers import BM25Retriever
-from langchain_community.retrievers import EnsembleRetriever
-from langchain.chains import ConversationalRetrievalChain
-from langchain.memory import ConversationBufferMemory
 from langchain_core.prompts import PromptTemplate
 from langchain_core.documents import Document
+from langchain.chains import ConversationalRetrievalChain
+from langchain.memory import ConversationBufferMemory
+
+try:
+    from langchain.retrievers import EnsembleRetriever
+except ImportError:
+    from langchain_community.retrievers import EnsembleRetriever
 
 # ---------- Embeddings ----------
 embeddings = HuggingFaceEmbeddings(