setGroup
Adds @self to the group of @group.
In a group of multiple toggle buttons, only one button can be active at a time.
Setting up groups in a cycle leads to undefined behavior.
Note that the same effect can be achieved via the iface@Gtk.Actionable API, by using the same action with parameter type and state type 's' for all buttons in the group, and giving each button its own target value.
Parameters
group
another GtkToggleButton
to form a group with