

TITLE
Add the ability to skip runtime version check

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2

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# 🚀 Feature request

Add the ability to skip version check / raise a warning instead of an error if the checks failed.

## Motivation

Currently, Transformers perform a runtime libraries version check and raise an error if some of the requirements has a version that is different from the specified.

While version check is a reasonable thing to do, an error seems like an overkill. As [I mentioned](https://github.com/huggingface/transformers/pull/8073#issuecomment-765632175) in #8073, this, for example, prevents from using the latest version of Tokenizers without modifying the source code.

## Your contribution

I suggest creating an environment variable (e.g. `TRANSFORMERS_VERSION_CHECK_STRICT`) that would control the reaction to a version mismatch. If it is set to `true`, the current behavior remains. If `false`, we log a warning instead of raising an error. Personally, I think that having this variable `false` by default will make it easier for the users to work in such cases.

What's your opinion in that? Probably we can find an even better solution together.