Add gtk4's list models

These are part of gtk4 so we must have an in-tree copy to use them with
gtk3. This is from gtk+4 commit ???
5 jobs for gtk-list-model in 4 minutes and 49 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #109442
librem5
build:native

00:01:23

 
  Test
passed #109443
librem5
test:native

00:01:11

passed #109444
librem5
test:smoke:one-output

00:01:58

passed #109445
librem5
test:smoke:two-outputs

00:02:07

 
  Package
passed #109446
librem5
package:deb

00:01:18