Use List instead of list (#13443)

Unify List usages in libs/langchain/langchain/text_splitter.py, only one
place it's `list`, all other ocurrences are `List`

libs/langchain/langchain/text_splitter.py

@@ -647,7 +647,7 @@ class Tokenizer:
     """Overlap in tokens between chunks"""
     tokens_per_chunk: int
     """Maximum number of tokens per chunk"""
-    decode: Callable[[list[int]], str]
+    decode: Callable[[List[int]], str]
     """ Function to decode a list of token ids to a string"""
     encode: Callable[[str], List[int]]
     """ Function to encode a string to a list of token ids"""