Space navigator doesn't indent subspaces clearly enough.

### Steps to reproduce

When scrolling around a hierarchical space tree in the space navigator view, it's very hard to distinguish subspaces from rooms, as they're only indented by a handful of pixels, despite the tree lines being rendered. I'd expect the subspaces to be much more noticeably indented.

### What happened?

Couldn't spot subspaces in order to join them.

### Operating system

macos

### Application version

nightly

### How did you install the app?

_No response_

### Homeserver

_No response_

### Have you submitted a rageshake?

No