Fix for AIStore client 1.23 (#1565)

Author: pzelasko

lhotse/serialization.py

@@ -793,7 +793,10 @@ class AIStoreIOBackend(IOBackend):
 
     def open(self, identifier: str, mode: str):
         client, version = get_aistore_client()
-        object = client.fetch_object_by_url(identifier)
+        try:
+            object = client.get_object_from_url(identifier)
+        except AttributeError:  # older AIStore client
+            object = client.fetch_object_by_url(identifier)
         if "r" in mode:
             try:
                 # AIStore >= 1.10.0