Update flake.lock

[github-actions[bot]]

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

Flake lock file updates:

• Updated input 'cachix/nixpkgs':
    'github:NixOS/nixpkgs/bd645e8668ec6612439a9ee7e71f7eac4099d4f6' (2024-01-02)
  → 'github:NixOS/nixpkgs/970a59bd19eff3752ce552935687100c46e820a5' (2023-09-17)

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