flake.lock: sync with the treefmt-nix follows fix

The follows retarget (previous commit) changed the input graph without
regenerating the lock; the first nix evaluation rewrote it in place,
leaving the tree dirty and tripping the cascade's dirty-guard
("working tree is dirty — refusing to bump", the 2026-07-17 rerun).
Ship the lock the inputs change should have carried.

:clown: Clown 0.3.22+1cb8383 — https://code.linenisgreat.com/clown/commit/1cb8383ef3006e1179952e14c7031d8ec2dc127e

Author: friedenberg