Strikethrough with <s> instead of <del> will be rendered as normal text

### Steps to reproduce

1. Send a message that uses [strikethrough via \](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/s) (e.g. with Cinny)
2. See the message being rendered like normal text.

### Outcome

#### What did you expect?
I'd expect the text to be stroked through.

#### What happened instead?
The text renders without any visual change.

### Your phone model

Google Pixel 7 Pro

### Operating system version

Android 15

### Application version and app store

Element X version 25.02.0

### Homeserver

Synapse 1.124.0

### Will you send logs?

Yes

### Are you willing to provide a PR?

No

Start by reproducing the issue in Element X version 25.02.0 with a message using HTML markup, then trace the message-rendering entry point in the Android app and its Matrix Rust SDK integration. Done means content is visibly struck through like content, with a regression test covering the reported case.

Written by the indexing model from the issue text.