use prompt.partial instead of bind for format_instructions

rag/chain.py

@@ -1,4 +1,4 @@
-from __future__ import annotations
+from __future__ import annotations
 
 from functools import lru_cache
 from typing import Any
@@ -36,7 +36,7 @@ def get_chain() -> Any:
         )
     )
     output_parser = PydanticOutputParser(pydantic_object=StructuredAnswer)
-    prompt_with_format = prompt.bind(
+    prompt_with_format = prompt.partial(
         format_instructions=output_parser.get_format_instructions()
     )