video/x-matroska is not considered a m.video type by Element when uploaded

### Steps to reproduce

1. Upload a video file to a room that's in mkv format.

### Outcome

#### What did you expect?

The file would be represented as a `m.video` event, allowing it to be played in-browser.

#### What happened instead?

The file was represented as a `m.file`, meaning users have to download the file to play it.

### Operating system

Arch Linux / Wayland w/ Sway

### Browser information

Firefox 102

### URL for webapp

develop.element.io

### Application version

Element version: 2032668e3a29-react-530b51a5ac4d-js-85a96c6467c2 Olm version: 3.2.8

### Homeserver

half-shot.uk

### Will you send logs?

Yes