PNG file uploaded from Element X Android shows as GIF in Element Web

### Steps to reproduce

1. Open Element X Android (version 0.2.3)
2. Upload a PNG file (I've only tried in an encrypted room, but I believe I've seen it in unencrypted rooms recently too)
3. Show the room in Element Web

### Outcome

#### What did you expect?

The image is shown without the "GIF" bit on its upper right corner.

#### What happened instead?

The image is shown with the "GIF" bit on its upper right corner. The full event sent by Element X Android (after decryption) is:

```json
{
"content": {
"body": "sticker_face.png",
"file": {
"hashes": {
"sha256": "0uLfzzYWro/qkQb51j7kZhleA4lIGq52/3OJRoFOeRY"
},
"iv": "0KQ/WCgxQrkAAAAAAAAAAA",
"key": {
"alg": "A256CTR",
"ext": true,
"k": "8GFwdb8OkVqmaYNV2tc6SagOIwWH5fv2ztXB6imM-2I",
"key_ops": [
"encrypt",
"decrypt"
],
"kty": "oct"
},
"url": "mxc://abolivier.bzh/ZGRHfcuIepVJDsQCvwpNsjVO",
"v": "v2"
},
"info": {
"h": 2069,
"mimetype": "image/png",
"size": 1579868,
"thumbnail_file": {
"hashes": {
"sha256": "b3FJZr2QsK67NCc/W0TGZfz0+U1zj2OHmzUUTLA46lo"
},
"iv": "OIdy2syoBbMAAAAAAAAAAA",
"key": {
"alg": "A256CTR",
"ext": true,
"k": "o35Lfo-UX8216XQ8Cz1Bezk7cda-oJYcCHsoQ9E09Cc",
"key_ops": [
"encrypt",
"decrypt"
],
"kty": "oct"
},
"url": "mxc://abolivier.bzh/SWSQJlyshkKPHjRdtqFmcXYF",
"v": "v2"
},
"thumbnail_info": {
"h": 689,
"mimetype": "image/jpeg",
"size": 29342,
"w": 498
},
"w": 1496,
"xyz.amorgan.blurhash": "KDB._#V@0f~VR*IV0eozn%"
},
"msgtype": "m.image"
},
"room_id": "!tfKoffUGXAVlVWhNYJ:abolivier.bzh",
"type": "m.room.message"
}
```

I'm not fully sure whether this belongs on the Element Web repo or on the Element X Android one. It only happens when I send the image from Element X Android, but Element Web is the only client I see recognising it as a GIF (Element Android (not X) does not show the play icon it shows for GIFs).

I've wondered for a bit whether this might just be https://github.com/vector-im/element-web/issues/24015, but it looks like a different issue since my image is sent with the `image/png` MIME type.

### Operating system

Arch Linux

### Browser information

Firefox 118.0.2

### URL for webapp

app.element.io

### Application version

Element version: 1.11.47, Olm version: 3.2.14

### Homeserver

abolivier.bzh

### Will you send logs?

Yes