chore: update flake.lock

[github-actions]

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

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/fcc147b1e9358a8386b2c4368bd928e1f63a7df2' (2023-07-13)
  → 'github:nixos/nixpkgs/f64b9738da8e86195766147e9752c67fccee006c' (2023-07-16)
• Updated input 'nixpkgs-unstable':
    'github:nixos/nixpkgs/2de8efefb6ce7f5e4e75bdf57376a96555986841' (2023-07-12)
  → 'github:nixos/nixpkgs/6cee3b5893090b0f5f0a06b4cf42ca4e60e5d222' (2023-07-16)

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