change list typing to comply w/ python 3.8

Author: João Leão

test/integration/persistent_bucket.py

@@ -11,6 +11,7 @@
 import os
 from dataclasses import dataclass
 from functools import cached_property
+from typing import List
 
 import backoff
 from b2sdk.v2 import Bucket
@@ -63,5 +64,5 @@ def get_or_create_persistent_bucket(b2_api: Api) -> Bucket:
     b2_api.bucket_name_log.append(bucket_name)
     return bucket
 
-def prune_used_files(b2_api: Api, bucket: Bucket, folders: list[str]):
+def prune_used_files(b2_api: Api, bucket: Bucket, folders: List[str]):
     b2_api.clean_bucket(bucket_object=bucket, only_files=True, only_folders=folders,ignore_retentions=True)