After ten days shall have elapsed from and after the date of the last publication of the Attorney General's notice provided for in section twenty-five of this article, if no proceeding be pending to have his approval of the bond issue reversed and modified, the Attorney General shall indorse upon each and every bond of the issue so approved by him his certificate to the effect that such bond has been approved by him by virtue of the authority vested in him by this article; that notice of his approval was published as required by section twenty-five of this article; that ten days have elapsed since the date of the last publication of such notice; that there has been no appeal from his decision to the Supreme Court of Appeals; and that the bond has become incontestable and is a binding obligation upon the authority issuing the same and upon the taxable property within the political division, and that the validity of such bond shall not be contested thereafter in any court or in any action or proceeding for any cause whatsoever.