LlamaTokenizerFast Fix (.., from_slow=True).
Author: Narsil
Pull request: yes

# What does this PR do?

`AutoTokenizer.from_pretrained(..., from_slow=True)`
and

` tokenizer.save_pretrained("./tmp")` 

wasn't working without those.

@ArthurZucker wants to add some tests for those.
I'm surprised by a few of these necessities since they seems quite standard defaults. 

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Fixes # (issue)


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Models:

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Comments:
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WIll add the tests in a followup PR 

So `test_save_slow_from_fast_and_reload_fast` tests this, but it was skipped. It should never be skipped. We should test with a minimal config exactly for the reason we just saw