They introduced[1] a GtkBox between the GtkEntry and the GtkComboBox to
add some magic in the layout computation.

[1] <https://git.gnome.org/browse/gtk+/commit/?id=222c43fc60362eeb97ce2d5e3a5583a69a2e30ef>
Signed-off-by: Quentin Glidic <sardemff7+git@sardemff7.net>