lib/tests/release.nix: Expose system parameter

lib/tests/release.nix

@@ -1,6 +1,7 @@
 { # The pkgs used for dependencies for the testing itself
   # Don't test properties of pkgs.lib, but rather the lib in the parent directory
-  pkgs ? import ../.. {} // { lib = throw "pkgs.lib accessed, but the lib tests should use nixpkgs' lib path directly!"; },
+  system ? builtins.currentSystem,
+  pkgs ? import ../.. { inherit system; } // { lib = throw "pkgs.lib accessed, but the lib tests should use nixpkgs' lib path directly!"; },
   # For testing someone may edit impure.nix to return cross pkgs, use `pkgsBuildBuild` directly so everything here works.
   pkgsBB ? pkgs.pkgsBuildBuild,
   nix ? pkgs-nixVersions.stable,