VoiceNextConnection.UserJoined event does not fire

[Alexejhero]

Describe the bug
VoiceNextConnection.UserJoined event callback does not fire, I subscribe to it but it never get executed

To Reproduce

1. Join a voicechannel and get a VoiceNextConnection
2. Subscribe to the UserJoined event
3. Have someone else join the channel

Expected behavior
The event should fire, but it doesnt

Additional context
This was also reported a few months ago in the discord

[Plerx2493]

Short investigastion shows that discord doesnt send OP12 (CLIENT_CONNECTED) anymore and sends OP18 and OP20 instead both of which arent documented

[Plerx2493]

[2023-12-05 19:37:01 +01:00] [308 /Voice ↓     ] [Trace] {"op":18,"d":{"user_id":"350967844957192192","flags":2}}
[2023-12-05 19:37:01 +01:00] [305 /VoiceDispatc] [Trace] Received unknown voice opcode (OP18)
[2023-12-05 19:37:01 +01:00] [308 /Voice ↓     ] [Trace] {"op":20,"d":{"user_id":"350967844957192192","platform":0}}
[2023-12-05 19:37:01 +01:00] [305 /VoiceDispatc] [Trace] Received unknown voice opcode (OP20)

[Plerx2493]

https://discord.com/developers/docs/change-log#experimenting-with-endtoend-encryption-for-voice-video

Could be related