bloom add_prefix_space= True
### System Info

Hi dear officer 
I use Bloom BloomTokenizerFast as a tokenizer. here is an issue.

Version =4.28.0
when I use BloomTokenizerFast, I find the add_prefix_space= True is not useful.
Here is the code. 
`tokenizer = BloomTokenizerFast.from_pretrained("bigscience/bloom",add_prefix_space = True)
print(tokenizer.add_prefix_space)
print(tokenizer("Hello world")["input_ids"])
print(transformers.__version__)
True
[59414, 8876]
4.28.0
`
here is other code. 
`from transformers import BloomTokenizerFast
tokenizer = BloomTokenizerFast.from_pretrained("bigscience/bloom")
print(tokenizer("Hello world")["input_ids"])
[59414, 8876]
`
I don't know why they will encode the same result. 

please have a look!
Thanks 

### Who can help?

@Arth

### Information

- [ ] The official example scripts
- [X] My own modified scripts

### Tasks

- [X] An officially supported task in the `examples` folder (such as GLUE/SQuAD, ...)
- [ ] My own task or dataset (give details below)

### Reproduction

It should encode different results. since add_prefix_space= True.

### Expected behavior

It should encode different results. since add_prefix_space= True.
cc @ArthurZucker and @younesbelkada <|||||>@younesbelkada @ArthurZucker <|||||>cc @ArthurZucker as he is more familiar than me regarding tokenizers<|||||>Hey! Thanks for opening this issue. This is half a `tokenizers` issue ( even if you save the tokenizer and modify the `tokenizer_config.json` to set `add_prefix_space=True` in the `pre_tokenizer` the outputs are the same) and half a transformers issue (setting `add_prefix_space=False` and then saving does not change the value saved!) 

Will try to fix it 👍🏻 