Livekit video calls are dropping after the upgrade to Element version 1.12.7 ["Widget Messaging leaking" bug]

### Steps to reproduce

1. Where are you starting? What can you see?
When connected to the Video room (Live kit), the connection drops, and the user reconnects at a random interval (seconds)
3. What do you click?
Just joined the call
5. More steps…

### Outcome

#### What did you expect?
Call to be stable.
#### What happened instead?
The call is dropping.

**When downgraded to 1.12.6, no issues with audio/video calls were detected.**

The Synapse server is reporting
[TXN OPERROR] {restart_delayed_event-26c2} could not serialize access due to concurrent update

The client is reporting a few messages with a decryption error; however, no messages were sent to the room:

```
{
"type": "m.room.message",
"content": {
"msgtype": "m.bad.encrypted",
"body": "** Unable to decrypt: DecryptionError: leading sigil is incorrect or missing at line 1 column 66 **"
}
}

```

### Operating system

Windows, MacOS

### Application version

Element version: 1.12.7 Crypto version: Rust SDK 0.14.0 (c3b7918), Vodozemac 0.9.0

### How did you install the app?

_No response_

### Homeserver

{"server":{"name":"Synapse","version":"1.143.0"}}

### Will you send logs?

Yes