Fix toggle mode of BaseButton.

..which got broken with #11480.

scene/gui/base_button.cpp

@@ -39,7 +39,9 @@ void BaseButton::_unpress_group() {
 	if (!button_group.is_valid())
 		return;
 
-	status.pressed = false;
+	if (toggle_mode) {
+		status.pressed = true;
+	}
 
 	for (Set<BaseButton *>::Element *E = button_group->buttons.front(); E; E = E->next()) {
 		if (E->get() == this)