Interpolated scrolling not working on low resolution and pixel perfect scroll devices

## What Happened

https://user-images.githubusercontent.com/39268094/131058720-ade1c8c8-a9e0-43b9-9fae-40950f0741a3.mp4

Using a low resolution scroll device (mouse scrollwheel) and hovering over the scroll bar to scroll (to get interpolated scrolling), scrolling does not work. Using a pixel perfect scroll device (touchpad) scrolls successfully at first, but shows the same phenomenon as in the video towards the end of the scroll (i.e. when my fingers leave the touchpad and kinetic scrolling kicks in). Non-interpolated scrolling using a low resolution scroll device (mouse scrollwheel) works fine.

P.S. please ignore the audio in the video

## Expected Behavior

The view should scroll correctly no matter what scrolling device I use

## Steps to Reproduce

1. Open Mail, with a long list of emails in inbox
2. With a mouse, hover over the scroll bar
3. Scroll
4. Repeat with touchpad, but do not hover over scroll bar
5. Repeat with mouse, but do not hover over scroll bar

### Logs

## Platform Information

io.elementary.mail 6.1.0+r613+pkg23~ubuntu6.1 amd64