GPT Neo Tokenizers can't change BOS or EOS token
## Environment info
<!-- You can run the command `transformers-cli env` and copy-and-paste its output below.
     Don't forget to fill out the missing fields in that output! -->

- Platform: Linux-5.8.0-55-generic-x86_64-with-debian-bullseye-sid
- Python version: 3.7.10
- PyTorch version (GPU?): 1.8.1 (True)
- Tensorflow version (GPU?): not installed (NA)
- Using GPU in script?: RTX 3090
- Using distributed or parallel set-up in script?: Using DeepSpeed

Conda env:
channels:
  - pytorch
  - nvidia
  - conda-forge
  - defaults
dependencies:
  - _libgcc_mutex=0.1=main
  - blas=1.0=mkl
  - bzip2=1.0.8=h7b6447c_0
  - ca-certificates=2021.5.30=ha878542_0
  - certifi=2021.5.30=py37h89c1867_0
  - cudatoolkit=11.1.74=h6bb024c_0
  - ffmpeg=4.3=hf484d3e_0
  - freetype=2.10.4=h5ab3b9f_0
  - gmp=6.2.1=h2531618_2
  - gnutls=3.6.15=he1e5248_0
  - intel-openmp=2021.2.0=h06a4308_610
  - joblib=1.0.1=pyhd8ed1ab_0
  - jpeg=9b=h024ee3a_2
  - lame=3.100=h7b6447c_0
  - lcms2=2.12=h3be6417_0
  - ld_impl_linux-64=2.33.1=h53a641e_7
  - libblas=3.9.0=9_mkl
  - libcblas=3.9.0=9_mkl
  - libffi=3.3=he6710b0_2
  - libgcc-ng=9.1.0=hdf63c60_0
  - libgfortran-ng=7.5.0=h14aa051_19
  - libgfortran4=7.5.0=h14aa051_19
  - libiconv=1.15=h63c8f33_5
  - libidn2=2.3.1=h27cfd23_0
  - liblapack=3.9.0=9_mkl
  - libpng=1.6.37=hbc83047_0
  - libstdcxx-ng=9.1.0=hdf63c60_0
  - libtasn1=4.16.0=h27cfd23_0
  - libtiff=4.2.0=h85742a9_0
  - libunistring=0.9.10=h27cfd23_0
  - libuv=1.40.0=h7b6447c_0
  - libwebp-base=1.2.0=h27cfd23_0
  - lz4-c=1.9.3=h2531618_0
  - mkl=2021.2.0=h06a4308_296
  - mkl-service=2.3.0=py37h27cfd23_1
  - mkl_fft=1.3.0=py37h42c9631_2
  - mkl_random=1.2.1=py37ha9443f7_2
  - ncurses=6.2=he6710b0_1
  - nettle=3.7.2=hbbd107a_1
  - numpy=1.20.2=py37h2d18471_0
  - numpy-base=1.20.2=py37hfae3a4d_0
  - olefile=0.46=py37_0
  - openh264=2.1.0=hd408876_0
  - openssl=1.1.1k=h27cfd23_0
  - pillow=8.2.0=py37he98fc37_0
  - pip=21.1.1=py37h06a4308_0
  - python=3.7.10=hdb3f193_0
  - python_abi=3.7=1_cp37m
  - pytorch=1.8.1=py3.7_cuda11.1_cudnn8.0.5_0
  - readline=8.1=h27cfd23_0
  - scikit-learn=0.23.2=py37hddcf8d6_3
  - scipy=1.5.3=py37h8911b10_0
  - setuptools=52.0.0=py37h06a4308_0
  - six=1.15.0=py37h06a4308_0
  - sqlite=3.35.4=hdfb4753_0
  - threadpoolctl=2.1.0=pyh5ca1d4c_0
  - tk=8.6.10=hbc83047_0
  - torchaudio=0.8.1=py37
  - torchvision=0.9.1=py37_cu111
  - typing_extensions=3.7.4.3=pyha847dfd_0
  - wheel=0.36.2=pyhd3eb1b0_0
  - xz=5.2.5=h7b6447c_0
  - zlib=1.2.11=h7b6447c_3
  - zstd=1.4.9=haebb681_0
  - pip:
    - chardet==4.0.0
    - click==8.0.1
    - datasets==1.7.0
    - deepspeed==0.4.0+8def3cb
    - dill==0.3.3
    - filelock==3.0.12
    - fsspec==2021.6.0
    - huggingface-hub==0.0.8
    - idna==2.10
    - importlib-metadata==4.5.0
    - multiprocess==0.70.11.1
    - ninja==1.10.0.post2
    - packaging==20.9
    - pandas==1.2.4
    - protobuf==3.17.3
    - psutil==5.8.0
    - pyarrow==3.0.0
    - pyparsing==2.4.7
    - python-dateutil==2.8.1
    - pytz==2021.1
    - regex==2021.4.4
    - requests==2.25.1
    - sacremoses==0.0.45
    - tensorboardx==1.8
    - tokenizers==0.10.3
    - tqdm==4.49.0
    - transformers==4.6.1
    - triton==0.4.2
    - urllib3==1.26.5
    - xxhash==2.0.2
    - zipp==3.4.1



### Who can help
@LysandreJik seems to be the one to tag as this is an issue with the tokenizer


## Information
When loading the GPT Neo tokenizer with either the GPT2Tokenizer, or with the AutoTokenizer, you are unable to change the EOS of BOS tokens through passing arguments

Model I am using: GPT Neo 2.7B and 1.3B  and its Tokenizer

The problem arises when using:
* [* ] my own modified scripts: (give details below)

The tasks I am working on is:
*[ *] my own task or dataset: (give details below)
I am trying to finetune the model using DeepSpeed and a custom dataset

## To reproduce

Steps to reproduce the behavior:

1. Load GPT Neo Tokenizer from pretrained using either AutoTokenizer or GPT2Tokenizer
2. Pass arguments to change EOS and BOS tokens
3. Print out the tokens using tokenizer.bos_token and tokenizer.eos_token
4. Notice that it has not changed
5. Do steps 1-3 for another model, say gpt2 and notice that it does change

```python
    tokenizer = AutoTokenizer.from_pretrained(
    "gpt2-xl",bos_token='<|beginoftext|>',
    eos_token='<|endoftext|>', pad_token='<|pad|>')
    print(tokenizer.bos_token)
    print(tokenizer.eos_token)
    print()
    tokenizer = AutoTokenizer.from_pretrained(
    "EleutherAI/gpt-neo-2.7B",bos_token='<|beginoftext|>',
    eos_token='<|endoftext|>', pad_token='<|pad|>')
    print(tokenizer.bos_token)
    print(tokenizer.eos_token)

    print()
    tokenizer = AutoTokenizer.from_pretrained(
    "EleutherAI/gpt-neo-1.3B",bos_token='<|beginoftext|>',
    eos_token='<|endoftext|>', pad_token='<|pad|>')
    print(tokenizer.bos_token)
    print(tokenizer.eos_token)
    quit()
```

That gives this:
Special tokens have been added in the vocabulary, make sure the associated word embeddings are fine-tuned or trained.
<|beginoftext|>
<|endoftext|>

Special tokens have been added in the vocabulary, make sure the associated word embeddings are fine-tuned or trained.
Special tokens have been added in the vocabulary, make sure the associated word embeddings are fine-tuned or trained.
<|endoftext|>
<|endoftext|>

Special tokens have been added in the vocabulary, make sure the associated word embeddings are fine-tuned or trained.
Special tokens have been added in the vocabulary, make sure the associated word embeddings are fine-tuned or trained.
<|endoftext|>
<|endoftext|>

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## Expected behavior
The expected behavior is that the values of the bos and eos tokens change.  It does not change though.

<!-- A clear and concise description of what you would expect to happen. -->

This issue has been automatically marked as stale because it has not had recent activity. If you think this still needs to be addressed please comment on this thread.

Please note that issues that do not follow the [contributing guidelines](https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md) are likely to be ignored.<|||||>Hi there, I just tried this but couldn't reproduce it. Here's the colab if you want to check https://colab.research.google.com/drive/1gGWMOdjF6wIVfUlo0XE1LfupY5T7ioVS?usp=sharing<|||||>I was using 4.6.1.  Perhaps its been fixed.  I ran your code as well and didn't see the issue.