Stickers aren't displayed in Safari

### Steps to reproduce

1. Open the "More options" menu
2. Select Sticker
3. Click "Add some now"
4. Add the packs you'd like
5. Close the modal
6. Repeat step 1 & 2
7. "Getting stickerpacks..." loads indefinitely

### Outcome

#### What did you expect?
Stickers should appear in the small modal after being added.

#### What happened instead?
No stickers appears and you wait indefinitely for the loading screen, even if it's working as intended on Element iOS.

Here are the console logs:
```js
[Error] Failed to load resource: the server responded with a status of 403 (Forbidden) (stickers-5fa3ecc75b9c6ba7a6e1.bundle.js.map, line 0)
```

### Operating system

macOS v12.6

### Browser information

Safari v16 (17614.1.25.9.10, 17614)

### URL for webapp

Private server

### Application version

Riot version: 1.11.0, Olm version: 3.2.8

### Homeserver

Synapse (unkown version)

### Will you send logs?

Yes