flake.lock: Update

Flake lock file updates:

• Updated input 'haskell-nix':
    'github:input-output-hk/haskell.nix/131f8cc' (2026-05-16)
  → 'github:input-output-hk/haskell.nix/62630c2' (2026-07-04)
• Updated input 'haskell-nix/hackage':
    'github:input-output-hk/hackage.nix/a482aef' (2026-05-16)
  → 'github:input-output-hk/hackage.nix/802e4ca' (2026-07-04)
• Updated input 'haskell-nix/hackage-for-stackage':
    'github:input-output-hk/hackage.nix/ab71329' (2026-05-16)
  → 'github:input-output-hk/hackage.nix/d59c86f' (2026-07-04)
• Updated input 'haskell-nix/iserv-proxy':
    'github:stable-haskell/iserv-proxy/3f7b281' (2026-04-08)
  → 'github:stable-haskell/iserv-proxy/8cdc446' (2026-05-10)
• Updated input 'haskell-nix/stackage':
    'github:input-output-hk/stackage.nix/c1f217f' (2026-05-16)
  → 'github:input-output-hk/stackage.nix/bdfd849' (2026-07-04)

Author: github-actions[bot]