Replace the new icon with a version without aliasing.
Generated by exporting part of https://github.com/pypy/pypy.org/blob/main/images/pypy-logo.svg as PNG at different sizes using Inkscape, then merging them into ICO using ImageMagick.
Comparison with old icon:
- Windows Explorer: https://pasteboard.co/JUnTTwA.png
- Taskbar: https://pasteboard.co/JUoba2J.png
(you might have to rename the file or kill and restart Windows Explorer to see the new icon locally)