Add missing max_length value to generation config

generation_config.json

@@ -7,6 +7,7 @@
   "bos_token_id": 50257,
   "decoder_start_token_id": 50258,
   "eos_token_id": 50257,
+  "max_length": 448,
   "pad_token_id": 50257,
   "transformers_version": "4.46.3"
 }