People Panel: Jumping scrollbar-thumb

### Steps to reproduce

Where are you starting? What can you see?
Right panel: People.

What do you click?
1- Scroll down to roughly 1/4 or more of the list.
2- Click the scrollbar track or thumb.

https://github.com/user-attachments/assets/7216ca40-e73c-4c2c-b763-a595e13fedb5

### Outcome

#### What did you expect?
To be able to grab the scrollbar-thumb.
Scrollbar thumb to move toward the clicked/grabbed point on the track.
#### What happened instead?
The thumb jumps to the top of the list then toward the clicked/grabbed point.

### Operating system

Linux MInt

### Application version

Element version: 1.12.24

### How did you install the app?

get-started

### Homeserver

matrix.org

### Will you send logs?

No

Start by reproducing the scrollbar interaction in the People panel on Linux Mint, using the listed Element version and steps. Trace the People panel's scrollbar or list interaction entry point and verify that clicking or grabbing the track moves the thumb directly toward the selected position without first jumping to the top.

Written by the indexing model from the issue text.