Move Stack to depend on Cabal-3.8.1.0

[mpilgrem]

The motivation is: (a) part of the preparation of moving Stack to GHC 9.4.x, which ships with Cabal-3.8.1.0; and (b) to assist with ##5839, which would be good to see in Stack 2.9.3.

[mpilgrem]

Currently blocked by hpack-0.35.0, which specifies Cabal < 3.7. See: sol/hpack#523