Make the regular update action update all flake inputs

[infinisil]

For the past 2 months, the Nixpkgs for the manuals was not updated because of this!

ZurichZHF

• Fixes https://github.com/NixOS/nixos-homepage/issues/1431
• Fixes https://github.com/NixOS/nix/issues/10743
• Fixes https://github.com/NixOS/nixos-homepage/issues/1412