Markdown Editor: Video elements are not rendered

HTML video elements are not rendered in the Markdown Editor.

## Steps to reproduce

1. Open a Markdown file containing a video element:

```html

```

2. Reopen the file with the Markdown Editor.

## Expected

The embedded video and its controls are rendered.

## Actual

The editor leaves an empty area where the video should be. Placing the cursor in that area only reveals the raw `` element.

https://github.com/user-attachments/assets/4279b229-12cb-423d-a89a-c824e0e95425
## Real-world test file

This can be reproduced with the [VS Code 1.138 release notes on the `vnext` branch](https://github.com/microsoft/vscode-docs/blob/vnext/release-notes/v1_138.md#celebrate-marking-sessions-as-done-preview) of `microsoft/vscode-docs`.

The **Celebrate marking sessions as done (Preview)** section contains:

```html

```

To validate the bug or a future fix, clone or update `microsoft/vscode-docs` on the `vnext` branch and open `release-notes/v1_138.md` in the Markdown Editor. The video at `release-notes/images/1_138/mark-as-done-confetti.mp4` should render in that section.