feat: update all inputs, only PR if specified inputs updated

[huantianad]

For updating my NixOS configuration, I would like to only update my flake input automatically on nixpkgs/nixos-unstable updates. However, when there is such an update, I would also like other inputs to be updated alongside it.

Unsure if this is outside the scope of the action, and it is I think possible to do it manually, but would be nice to have it here instead.