Uploading captions should accept SRT files

[RubenQ42]

Describe the bug

When adding captions, only .vtt and text/vtt are accepted, while .srt is also supported by mux.

To Reproduce

Steps to reproduce the behavior:

1. Go to the details dialog of a Mux video
2. Click on 'Add caption'
3. Click on Select File
4. Confirm that the file browser only accepts .vtt files by default

Expected behavior

Both .srt and .vtt files should be accepted by the file browser, as both are supported by the Mux captions uploader.

Which versions of Sanity are you using?

sanity@5.10.0
sanity-plugin-mux-input@2.15.0

[R-Delfino95]

Hi! Thanks for reporting this.
I'll review the issue and get back to you soon