Fix Issue #29817 Video Classification Task Guide Using Undeclared Variables
Author: manju-rangam
Pull request: yes

# This PR fixes the following [issue #29817](https://github.com/huggingface/transformers/issues/29817)

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**Fixes # 29817**

Updates the Video_Clasification.md file to define the value of the variable **all_video_file_paths**

## Before submitting
- [ x] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


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@amyeroberts 
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Comments:
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/transformers/pr_30457). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update.

@amyeroberts , fixed your comments, thank you.

Thanks again for fixing! ❤️