Debian's webkit2gtk currently has to build itself 3 times:
- GTK3 with libsoup2.4 - the 4.0 API
- GTK3 with libsoup3 - the 4.1 API (no other change except the libsoup switch)
- GTK4 with libsoup3

We want to drop the 4.0 API and speed up the webkit2gtk builds.

Since formiko doesn't use libsoup directly or any other libraries that
use it, this is a simple switch.

Merge proposal at:
https://github.com/ondratu/formiko-debian/pull/2

Thank you,
Jeremy Bicha