flake.lock: Update (#928)

Flake lock file updates:

• Updated input 'devenv':
    'github:cachix/devenv/d59d872' (2026-06-18)
  → 'github:cachix/devenv/3d39d08' (2026-06-26)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/a037402' (2026-06-11)
  → 'github:NixOS/nixpkgs/4062d36' (2026-06-25)

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

Author: brianmay-actions