'WhisperTokenizer' object has no attribute 'set_prefix_tokens'
### System Info

- `transformers` version: 4.24.0
- Platform: Linux-5.15.0-52-generic-x86_64-with-glibc2.27
- Python version: 3.9.15
- Huggingface_hub version: 0.11.0
- PyTorch version (GPU?): 1.13.0 (True)
- Tensorflow version (GPU?): not installed (NA)
- Flax version (CPU?/GPU?/TPU?): not installed (NA)
- Jax version: not installed
- JaxLib version: not installed
- Using GPU in script?: Yes
- Using distributed or parallel set-up in script?: Yes

### Who can help?

@LysandreJik

### Information

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

### Tasks

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

### Reproduction

from transformers import WhisperTokenizer
tokenizer = WhisperTokenizer.from_pretrained("openai/whisper-medium", language="spanish", cache_dir="./pretrained_models")
tokenizer.set_prefix_tokens(language="english")

AttributeError: 'WhisperTokenizer' object has no attribute 'set_prefix_tokens'

### Expected behavior

![image](https://user-images.githubusercontent.com/75082385/204983801-7b23dffc-5e52-4dca-a625-e7d9cf8e8745.png)

This method should exist according to the documentation
Hi @nethermanpro, I'm not a maintainer, but I think I know what is going on.  

It seems that in `transformers 4.24.0`, the method  `set_prefix_tokens` is not present in this version. You can find it in this repository in the main branch, if you want to use it, you will need to install transformers directly from this repository `pip install git+https://github.com/huggingface/transformers.git` or wait for the next stable release. 

The documentation you are looking at seems to be https://huggingface.co/docs/transformers/main/en/model_doc/whisper which is the documentation of the main branch, to check the documentation of `4.24.0` you can 
select it at the top left dropdown where it says `main`. 

Here you have the link https://huggingface.co/docs/transformers/v4.24.0/en/model_doc/whisper#transformers.WhisperTokenizer

<|||||>Thanks, I think that solves my problem.