Add gdbus.exe to Synfig Windows package

[ice0]

DBus is a necessary component of the GTK stack.

The gdbus binary is needed to create a session bus on Windows, which doesn’t have a DBus server spawned automatically when the session starts. When GTK tries to acquire the application’s name on the session bus, it will spawn the DBus server provided by GIO on Windows. The component responsible for searching the gdbus.exe binary is GIO, not GTK.

The gdbus.exe binary should be installed in the same directory as the GIO DLL.

https://discourse.gnome.org/t/gtk-warning-about-gdbus-exe-not-being-found-on-windows-msys2/2893