deps: update flake.lock (#126)

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/80d50fc87924c2a0d346372d242c27973cf8cdbf?narHash=sha256-3u6rEbIX9CN/5A5/mc3u0wIO1geZ0EhjvPBXmRDHqWM%3D' (2025-06-27)
  → 'github:nixos/nixpkgs/c860cf0b3a0829f0f6cf344ca8de83a2bbfab428?narHash=sha256-4E7wWftF1ExK5ZEDzj41%2B9mVgxtuRV3wWCId7QAYMAU%3D' (2025-07-04)

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: mrcjkb