flake.lock: Update

Flake lock file updates:

• Updated input 'flake-parts':
    'github:hercules-ci/flake-parts/3107b77' (2026-04-01)
  → 'github:hercules-ci/flake-parts/f7c1a2d' (2026-05-13)
• Updated input 'haskell-flake':
    'github:srid/haskell-flake/f52ac89' (2026-04-21)
  → 'github:srid/haskell-flake/375c8e3' (2026-05-17)
• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/a23094b' (2026-05-01)
  → 'github:nixos/nixpkgs/501880c' (2026-06-01)

Author: github-actions[bot]