flake.lock: Update (#146)

Flake lock file updates:

• Updated input 'neovim-nightly':
    'github:neovim/neovim/36552adb39edff2d909743f16c1f061bc74b5c4e?dir=contrib' (2023-12-14)
  → 'github:neovim/neovim/f4f7e294695abe7837af62b68564114de7abd0b4?dir=contrib' (2023-12-15)
• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/e97b3e4186bcadf0ef1b6be22b8558eab1cdeb5d' (2023-12-11)
  → 'github:nixos/nixpkgs/aa9d4729cbc99dabacb50e3994dcefb3ea0f7447' (2023-12-14)

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