nixos/services.tarsnap: fix escapeSystemdPath

[wahjava]

Description of changes

Fix for following error:

   error: attribute 'lib' missing

   at /nix/store/cjz8w4dgc3rd2n3dqv5c208vygndjyba-source/nixos/modules/services/backup/tarsnap.nix:90:49:

       89|                 type = lib.types.nullOr lib.types.path;
       90|                 default = "/var/cache/tarsnap/${utils.lib.escapeSystemdPath config.keyfile}";
         |                                                 ^
       91|                 defaultText = lib.literalExpression ''

introduced by e53c595 (#335631)

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/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 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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