Mac: End key unreliable

### Steps to reproduce

The "End" key doesn't work reliably on my machine.

1. Open a room with a decent amount of history.
2. Start scrolling up (such as with the scroll wheel). It appears that this bug is only triggered when you scroll up enough that it shows the "loading" spinner thingy, so keep scrolling until you see that.
3. Press the End key on the keyboard.

### What happened?

### What did you expect?
I expected this to return to the latest message in the room.

### What happened?
It scrolled down, but by a seemingly-random amount. I had to press End multiple times to get to the bottom.

I noticed that https://github.com/vector-im/element-web/issues/3232 mentions using Ctrl-End to jump to the bottom, and this appears to work correctly (I believe that that's the standard key combination for this action on Windows). However, I'd expect a Mac app to scroll all the way to the end when I press End by itself.

### Operating system

macOS 11.4

### Application version

Element 1.8.2

### How did you install the app?

From https://element.io/get-started

### Homeserver

matrix.org

### Have you submitted a rageshake?

No

Reproduce this in the macOS app using a room with enough history to trigger the loading spinner, then inspect the End-key scrolling behavior around that loading state. Done means pressing End once consistently returns to the latest message, matching the expected behavior without requiring repeated presses.

Written by the indexing model from the issue text.