Fix `model_max_length` in `tokenizer_config.json`

The current value of `model_max_length` in `tokenizer_config.json`(basically infinity) is inconsistent with `max_position_embeddings` in `config.json`. It's also inconsistent with that of `bge-base-en`.

This also happens with `bge-small-en`, but I was thinking that it was good to have any potential discussion here first, before sending a PR for that one as well.

tokenizer_config.json

@@ -4,7 +4,7 @@
   "do_basic_tokenize": true,
   "do_lower_case": true,
   "mask_token": "[MASK]",
-  "model_max_length": 1000000000000000019884624838656,
+  "model_max_length": 512,
   "never_split": null,
   "pad_token": "[PAD]",
   "sep_token": "[SEP]",