Update tokenizer_config.json

There is no GPTNeoXTokenizer, only GPTNeoXTokenizerFast it seems
See https://github.com/huggingface/transformers/issues/17756

tokenizer_config.json

@@ -4,6 +4,6 @@
   "eos_token": "<|endoftext|>",
   "name_or_path": "EleutherAI/gpt-neox-20b",
   "special_tokens_map_file": "/admin/home-hailey/.cache/huggingface/hub/models--EleutherAI--gpt-neox-20b/snapshots/4e49eadb5d14bd22f314ec3f45b69a87b88c7691/special_tokens_map.json",
-  "tokenizer_class": "GPTNeoXTokenizer",
+  "tokenizer_class": "GPTNeoXTokenizerFast",
   "unk_token": "<|endoftext|>"
 }