Switch to libsoup 3
Please switch gthumb 3 from libsoup 2.4 to libsoup3.
This also requires switching from webkitgtk 4.0 to 4.1 (at least there the API didn't change except that libsoup3 is used now).
If you want gthumb to be used on older distros, you may need to keep an option to build gthumb with libsoup 2.