The "your message can't be sent; retry/discard" prompt doesn't push the timeline up.

### Steps to reproduce

1. Unplug your internet
2. Try to send a message in a room
3. Note that the "can't be sent" warning pops up over the top of the message you just sent. It should (and used to) push the timeline up, but now the scroll position isn't preserved, so the prompt covers the message you just sent, making it superficially look like the message was eaten.

### Outcome

#### What did you expect?

Timeline scroll offset should be preserved even if we pop up messages at the bottom of the timeline.

#### What happened instead?

Timeline scroll offset is preserved relative to the bottom of the window, not the bottom of the prompt, making the prompt occlude the timeline and effectively "scroll up" the timeline without you performing a scroll operation.

### Operating system

macOS 13.1

### Application version

nightly desktop

### How did you install the app?

_No response_

### Homeserver

matrix.org

### Will you send logs?

No