flake.lock: Update

[github-actions]

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

Flake lock file changes:

• Updated input 'nixpkgs':
    'github:NixOS/nixpkgs/8a308775674e178495767df90c419425474582a1' (2021-11-29)
  → 'github:NixOS/nixpkgs/29d1f6e1f625d246dcf84a78ef97b4da3cafc6ea' (2021-11-30)

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