CircularProgress value is scaled incorrectly

[Robotino04]

Describe the bug
A value of 0.5 (or half filled) renders as follows instead of actually filling one half:

To Reproduce

<circularprogress
    value={0.5}
    startAt={0.3}
    endAt={1}
    rounded={true}
    heightRequest={50}
    widthRequest={50}
    css={"font-size: 5px; background-color: red;"}
></circularprogress>

Expected behavior
The filled part divides the background in half.

Additional context

astal/lib/astal/gtk3/src/widget/circularprogress.vala

Line 121 in 4c19d8d

var scaled = arc_length + value;

Should be something like this I think.

var scaled = value / arc_length + start; 

I would test it myself, but I'm not sure how to get ags run to use a modified build of astal on NixOS.