§ 5.   Irrepealable tax to repay debt of municipality or political subdivision. Any city, county, town, school district or any other subdivision incurring indebtedness shall, at or before the time of so doing, provide for the collection of an annual tax sufficient to pay the interest and also the principal thereof when due, and all laws or ordinances providing for the payment of the interest or principal of any debt shall be irrepealable until such debt be paid.