chore: update flake.lock

[mrcjkb]

Automated changes by the update-flake-lock GitHub Action.

Flake lock file updates:

• Updated input 'neovim-nightly':
    'github:neovim/neovim/184f8423492f62b67b499efc53582dad4917ca5a?dir=contrib' (2023-12-19)
  → 'github:neovim/neovim/104565909798eff57d0bd46c56d149055b8a739b?dir=contrib' (2023-12-21)
• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/dd8e82f3b4017b8faa52c2b1897a38d53c3c26cb' (2023-12-18)
  → 'github:nixos/nixpkgs/7c33cd6bf01cf09f77bfdf6741cddfffa2cd5640' (2023-12-20)

Running GitHub Actions on this PR

GitHub Actions will not run workflows on pull requests which are opened by a GitHub Action.

To run GitHub Actions workflows on this PR, run:

git branch -D update_flake_lock_action
git fetch origin
git checkout update_flake_lock_action
git commit --amend --no-edit
git push origin update_flake_lock_action --force