Bug#1081894: railway-gtk FTBFS: build-depends on no-longer-existing version

[Rebecca N. Palmer]

Control: tags -1 patch
(but a risky one, see below)

This FTBFS is because Rust -dev packages are versioned: it's 
librust-gdk4-0.9+default-dev now.  Updating the versions makes it build:
https://salsa.debian.org/rnpalmer-guest/railway-gtk/-/tree/debian/trixie?ref_type=heads

However, I have *not* tested the resulting package (it has no build-time 
tests), and this is risky because those version numbers imply potential 
incompatibility.  In particular, we may need 
https://salsa.debian.org/gnome-team/railway-gtk/-/blob/debian/latest/debian/patches/gtk-rs-0.9.patch?ref_type=heads

(The 2.7 on the debian/latest branch would be better if it worked, but 
currently doesn't build, probably because some other dependencies are 
too *old* i.e. #1075816.)