Add model_max_length argument to avoid warnings

tokenizer_config.json

@@ -1 +1 @@
-{"add_special_tokens": false, "special_tokens_map_file": null, "full_tokenizer_file": null}
+{"add_special_tokens": false, "special_tokens_map_file": null, "full_tokenizer_file": null, "model_max_length": 512}