deps: update flake.lock (#122)

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/59138c7667b7970d205d6a05a8bfa2d78caa3643?narHash=sha256-7gGa49iB9nCnFk4h/g9zwjlQAyjtpgcFkODjcOQS0Es%3D' (2025-05-31)
  → 'github:nixos/nixpkgs/a4ff0e3c64846abea89662bfbacf037ef4b34207?narHash=sha256-UAaWOyQhdp7nXzsbmLVC67fo%2BQetzoTm9hsPf9X3yr4%3D' (2025-06-06)

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

Author: mrcjkb