Fix Upload Button

[freddyaboulton]

Description

The upload button was not properly handling the case of multiple files. Going to test in colab once the PR wheel gets built.

Closes: #3729, Closes: #3790

Edit: Works in colab!

Checklist:

• I have performed a self-review of my own code
• I have added a short summary of my change to the CHANGELOG.md
• My code follows the style guidelines of this project
• I have commented my code in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

A note about the CHANGELOG

Hello 👋 and thank you for contributing to Gradio!

All pull requests must update the change log located in CHANGELOG.md, unless the pull request is labeled with the "no-changelog-update" label.

Please add a brief summary of the change to the Upcoming Release > Full Changelog section of the CHANGELOG.md file and include
a link to the PR (formatted in markdown) and a link to your github profile (if you like). For example, "* Added a cool new feature by [@myusername](link-to-your-github-profile) in [PR 11111](https://github.com/gradio-app/gradio/pull/11111)".

If you would like to elaborate on your change further, feel free to include a longer explanation in the other sections.
If you would like an image/gif/video showcasing your feature, it may be best to edit the CHANGELOG file using the
GitHub web UI since that lets you upload files directly via drag-and-drop.

[gradio-pr-bot]

All the demos for this PR have been deployed at https://huggingface.co/spaces/gradio-pr-deploys/pr-3782-all-demos

[dawoodkhan82]

LGTM, tested and works

[freddyaboulton]

Thanks so much @dawoodkhan82 !