neofetch: improve detect NixOS version

[Izorkin]

Description of changes

Improve detect NixOS version

Before PR:

neofetch --off --distro_shorthand on | grep OS
OS: nixos 22.11 x86_64

neofetch --off --distro_shorthand tiny | grep OS
OS: nixos x86_64

neofetch --off --distro_shorthand off | grep OS
OS: NixOS 22.11 (Raccoon) x86_64

After PR:

neofetch --off --distro_shorthand on | grep OS
OS: NixOS 22.11 (Raccoon) x86_64

neofetch --off --distro_shorthand tiny | grep OS
OS: NixOS x86_64

neofetch --off --distro_shorthand off | grep OS
OS: NixOS 22.11.git.31109649164 (Raccoon) x86_64

PR in upstream - dylanaraps/neofetch#2157

cc @erikrodrgz @Artturin @rhoriguchi @lilyinstarlight @SuperSandro2000

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 22.11 Release Notes (or backporting 22.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

[Izorkin]

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