Windows installer migration to windows-2025 images

[anaegel]

The image windows-2025 (aka windows-latest) does not support NSIS anymore. As a workaround, installers are now build using the (old) windows-2022. More details here:

https://github.com/actions/runner-images
https://nsis.sourceforge.io/Main_Page

Ideas for a future strategy (manual install of NSIS, alternative installer, ...) are welcome.

[anaegel]

This issue is a continuation of #6