syncstorage-rs: link up firefox-syncserver test

pkgs/by-name/sy/syncstorage-rs/package.nix

@@ -8,6 +8,7 @@
   makeBinaryWrapper,
   lib,
   nix-update-script,
+  nixosTests,
 }:
 
 let
@@ -54,6 +55,8 @@ rustPlatform.buildRustPackage rec {
 
   passthru.updateScript = nix-update-script { };
 
+  passthru.tests = { inherit (nixosTests) firefox-syncserver; };
+
   meta = {
     description = "Mozilla Sync Storage built with Rust";
     homepage = "https://github.com/mozilla-services/syncstorage-rs";