Describe the bug

Normal users usually get UIDs in the range of >=1000 when the Perl-based users script is activated:

This is not the case when systemd.sysusers.enable is enabled, as new normal users may receive a UID in the range of <1000.

Steps To Reproduce

Steps to reproduce the behavior:

1. Open systemd-sysusers-mutable.nix test.
2. Add the following line at the end of the "normalo user is created" subtest:
   print(machine.succeed("id -u normalo"))
3. Run the test using nix -L build .#nixosTests.systemd-sysusers-mutable

Expected behavior

UID allocation behavior is the same as in the Perl users script.

Notify maintainers

@nikstur

Metadata

Please run nix-shell -p nix-info --run "nix-info -m" and paste the result.

 - system: `"x86_64-linux"`
 - host os: `Linux 6.9.7-xanmod1, NixOS, 24.05 (Uakari), 24.05.20240702.706eef5`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.22.2`
 - nixpkgs: `/etc/nix/inputs/nixpkgs`

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