There's nothing illegal going on.

Buying Laptops for Lancaster ISD students isn't illegal.

Borrowing money for thirty years isn't illegal.

Borrowing money for thirty years to buy laptops that last three is ...

Well, I dunno. Do you?

I think it's pretty hard to pass a law against "stupid." Frankly I'm of the opinion we all have a inalienable birthright as Americans to be stupid. (If there ever was a law against stupid, I know I would be in big trouble...)

The laws about what Texas schools can use bond funds for The relevant laws are hyperlinked
here ,

each common school district under its jurisdiction, may:
(1) issue bonds for:
(A) the construction, acquisition, and equipment of school buildings in the district;
(B) the acquisition of property or the refinancing of property financed under a contract entered under Subchapter A, Chapter 271, Local Government Code, regardless of whether payment obligations under the contract are due in the current year or a future year;
(C) the purchase of the necessary sites for school buildings; and
(D) the purchase of new school buses; and
(2) may levy, pledge, assess, and collect annual ad valorem taxes sufficient to pay the principal of and interest on the bonds as the principal and interest become due, subject to Section 45.003.

Also here .
32.105. EXPENDITURE OF PUBLIC FUNDS. A school district or open-enrollment charter school may spend public funds to: (1) purchase, refurbish, or repair any data processing equipment transferred to a student under this subchapter; and (2) store, transport, or transfer data processing equipment under this subchapter.

and here.
§ 32.202. LIMITATION ON CERTAIN FUNDS. A public school that provides a computer used to access the Internet is not eligible for a loan or grant under Subchapter C, Chapter 57, Utilities Code, unless the school adopts and implements an Internet safety policy under this section or under the federal Children's Internet Protection Act

Oh, and maybe here.

§ 143.005. FUNDS. (a) The technology program is funded by appropriations and by gifts, grants, and donations made for that purpose.

Go help me find where we are allowed to use borrowed money for laptops. Maybe, if you're smarter than I am, you can figure it out.