flake.lock: Update (#907)

Flake lock file updates:

• Updated input 'devenv':
    'github:cachix/devenv/d5e9138' (2026-06-01)
  → 'github:cachix/devenv/90ed622' (2026-06-05)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/b51242d' (2026-05-31)
  → 'github:NixOS/nixpkgs/6b31628' (2026-06-03)

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

Author: brianmay-actions