Any bonds reciting that they are issued pursuant to this chapter shall, in any action or proceeding involving their validity, be conclusively deemed to be fully authorized by this chapter and to have been issued, sold, executed and delivered in conformity herewith and with all other provisions of statutes applicable thereto and shall be incontestable, unless such action or proceeding is begun within sixty days after the approval of their sale by the vote specified in section 7-382.