Iphone Stickers sending as generic emojis

### Steps to reproduce

1. Where are you starting? What can you see?
Any matrix chat

3. What do you click?
On Keyboard > Emoji > Select any sticker in emojis or in the stickers section

4. More steps…

### Outcome

#### What did you expect?
The sticker to be sent as an image with no background

OR

The image to be turned into a sticker in a sticker pack, named and linked by the user, if possible.

#### What happened instead?
invisible character will appear in message box. When sent, the emoji will have the generic emoji character

### Your phone model

Iphone 15

### Operating system version

iOS18.7.8

### Application version

26.04.1

### Homeserver

Continuwuity 0.5.7 (selfhosted)

### Will you send logs?

Yes