Make the `/file` secure against file traversal attacks

Gradio is an open-source Python package that allows you to quickly build a demo or web application for your machine learning model, API, or any arbitary Python function. Versions of `gradio` prior to 4.11.0 contained a vulnerability in the `/file` route which made them susceptible to file traversal attacks in which an attacker could access arbitrary files on a machine running a Gradio app with a public URL (e.g. if the demo was created with `share=True`, or on Hugging Face Spaces) if they knew the path of files to look for. This issue has been patched in version 4.11.0.