Update flake.lock

[simonrw]

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

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/2c7f3c0fb7c08a0814627611d9d7d45ab6d75335' (2023-12-04)
  → 'github:nixos/nixpkgs/a9bf124c46ef298113270b1f84a164865987a91c' (2023-12-11)

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

[coveralls]

coverage: 76.809%. remained the same
when pulling 867761a on update_flake_lock_action
into 8bc8c31 on main.