switch-to-configuration-ng: add switchTest to passthru.tests

This makes ofborg more helpful in CI.

pkgs/by-name/sw/switch-to-configuration-ng/package.nix

@@ -3,6 +3,7 @@
   clippy,
   dbus,
   lib,
+  nixosTests,
   pkg-config,
   rustPlatform,
 }:
@@ -29,6 +30,8 @@ rustPlatform.buildRustPackage {
     cargo clippy -- -Dwarnings
   '';
 
+  passthru.tests = { inherit (nixosTests) switchTest; };
+
   meta = {
     description = "NixOS switch-to-configuration program";
     mainProgram = "switch-to-configuration";