flake.lock: Update (#920)

Flake lock file updates:

• Updated input 'devenv':
    'github:cachix/devenv/5f5109c' (2026-06-11)
  → 'github:cachix/devenv/d59d872' (2026-06-18)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/bd0ff2d' (2026-06-08)
  → 'github:NixOS/nixpkgs/a037402' (2026-06-11)

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Author: brianmay-actions