Changes the value of max_tab_name_length in dconf

def on_max_tab_name_length_changed(self, spin):
        """Changes the value of max_tab_name_length in dconf
        """
        val = int(spin.get_value())
        self.settings.general.set_int('max-tab-name-length', val)
        self.prefDlg.update_vte_subwidgets_states()