why set masked_bias as -10000 in GPT2
## Information

`masked_bias` is set as `-10000` in GPT2, why not `-inf`?

https://github.com/huggingface/transformers/blob/e43f3b6190cfd98a38912411b8bc8ecbb6629280/src/transformers/models/gpt2/modeling_gpt2.py#L133

## openai/gpt-2

In [openai/gpt2](https://github.com/openai/gpt-2/blob/a74da5d99abaaba920de8131d64da2862a8f213b/src/model.py#L88), the bias is set as `-1e10` 
```py
w = w*b - tf.cast(1e10, w.dtype)*(1-b)
```
## Other implementation, such as bert, transformer

https://github.com/huggingface/transformers/blob/82498cbc37d5c15520c7bddde5d804c804eee498/src/transformers/models/bart/modeling_bart.py#L81

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