Backgrounding app in 1:1 call kills audio stream

### Steps to reproduce

1. Start 1:1 call from anywhere in app
2. Switch apps or turn off screen

### Outcome

#### What did you expect?

Call should continue as normal

#### What happened instead?

Audio stops transmitting, will not resume even when bringing the app back to the foreground

### Your phone model

iPhone 13

### Operating system version

15.6.1

### Application version

1.9.7

### Homeserver

Synapse 1.68.0

### Will you send logs?

Yes