Fix bug leading to missing token in GPTSanJapaneseTokenizer
# Fixes the missing comma (,) token in the GPTSanJapaneseTokenizer

The comma character "," is a token in the default vocabulary file used by GPTSanJapaneseTokenizer.

However, the vocab file parser has a bug that deletes this token and so the GPTSanJapaneseTokenizer encodes commas as the <byte 44> token instead of a unique token.

This fixes that bug.

@tanreinama @younesbelkada @ArthurZucker 
Hey! Could you make sure to run `make fix-copies` ! Otherzise looks good to me<|||||>😅 sorry, you can remove the `copied from` to get rid of the issue with make fix copies overwriting<|||||>Remove this : `# Copied from transformers.models.gpt_neox_japanese.tokenization_gpt_neox_japanese.load_vocab_and_emoji`<|||||>The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_23883). All of your documentation changes will be reflected on that endpoint.