(g)where in respect of any proceeding relating to any tax year beginning before the 1st April, 2026,—(i)a refund falls due after commencement of this Act; or(ii)default is made after such commencement in the payment of any sum due under such proceeding, the provisions of this Act, relating to interest payable by the Central Government on refunds and interest payable by the assessee for default, shall apply for the period after the commencement of this Act;