Refine parameter type annotations
Author: flashJd
Pull request: yes

# What does this PR do?

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https://github.com/huggingface/transformers/pull/36644 this pr is blocked in `Checking for the ability to merge automatically`, maybe github issue, so I closed it and opened a new pr.

This PR refines the parameter type annotations in the add_tokens and add_special_tokens methods.special_tokens_dict parameter accept list or tuple when key is additional_special_tokens, but parameter type not covered.
The goal is to make the parameter type more clear


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Comments:
Hi 👋, thank you for opening this pull request! The pull request is converted to draft by default. The CI will be paused while the PR is in draft mode. When it is ready for review, please click the `Ready for review` button (at the bottom of the PR page). This will assign reviewers and trigger CI.

> Yep, this is correct. Thank you for your patience with this, and sorry about the weird Github issues before - I'm not sure why that happened!

I rebased my branch and force pushed to solve the `build_pr_documentation` ci failure caused by https://github.com/huggingface/transformers/pull/37393, but other tests failure occured which was passed before, can you collaborate to rebase to a commit_id which the baseline ci can run successfully, thx

The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_37666). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

CI is finally green after we did some fixes - thank you for your patience with that, and hopefully it won't take quite so long in future!