flake.lock: Update

[github-actions]

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

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/e06bd4b64bbfda91d74f13cb5eca89485d47528f' (2022-10-12)
  → 'github:NixOS/nixpkgs/ac20a8605b0f79be2d65d995cd347251cd5b984b' (2022-10-21)

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