Visual Studio builds: Update glibmm ABI version
Visual Studio builds: Update glibmm ABI version

The glibmm ABI version was updated in its unstable development series,
so we ought to reflect that here as well in our projects, as we await
for GTK+-4.0.

GNOME/gtkmm,GNOME/gtkmm,GNOME/gtkmm,GNOME/gtkmm