nixos-rebuild: fixed man page typo

[Andrew15-5]

I was RTFM and found --- CLI option which immediately caught my attention. After which I was surprised that in source you need to use one minus instead of two. And this is also the only place in the whole repo where rg '.Fl --' found a match.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• 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/)
• 25.05 Release Notes (or backporting 24.11 and 25.05 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
• Fits CONTRIBUTING.md.

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[SuperSandro2000]

Please take a look at the contributing guide. We don't do semantic commits.

[Andrew15-5]

Yeah, I'm not sure if I forgot or was it one of the first patches. I see the related section in pkgs/README.md.

But maybe I just looked that a bunch of other commits were structured like that, so I did the same. 128 commits: git log --oneline | rg '^\w+ (docs?|nix|nixos|feat|build|update|fix|tweak)\(.*?\):' (some of them are custom?).