Nothing in sections 70-644 to 70-653.02 contained shall prevent the district from assigning, pledging, or otherwise hypothecating, its revenue, incomes, receipts, or profits to secure the payment of indebtedness to the federal government; Provided, that the State of Nebraska shall never pledge its credit or funds, or any part thereof, for the payment or settlement of any indebtedness or obligation whatsoever of any district created under or subject to the provisions of Chapter 70, article 6.