flake.lock: Update

Flake lock file updates:

• Updated input 'flake-parts':
    'github:hercules-ci/flake-parts/59cf3f1447cfc75087e7273b04b31e689a8599fb' (2023-08-01)
  → 'github:hercules-ci/flake-parts/7f53fdb7bdc5bb237da7fefef12d099e4fd611ca' (2023-09-01)
• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/cf73a86c35a84de0e2f3ba494327cf6fb51c0dfd' (2023-08-10)
  → 'github:NixOS/nixpkgs/517501bcf14ae6ec47efd6a17dda0ca8e6d866f9' (2023-09-27)
• Updated input 'treefmt-nix':
    'github:numtide/treefmt-nix/19dee4bf6001849006a63f3435247316b0488e99' (2023-08-12)
  → 'github:numtide/treefmt-nix/720bd006d855b08e60664e4683ccddb7a9ff614a' (2023-09-27)