nixos/tests: add test for firejail

pkgs/os-specific/linux/firejail/default.nix

@@ -1,4 +1,4 @@
-{stdenv, fetchurl, fetchpatch, which}:
+{stdenv, fetchurl, fetchpatch, which, nixosTests}:
 let
   s = # Generated upstream information
   rec {
@@ -76,6 +76,8 @@ stdenv.mkDerivation {
   # bash: src/fsec-optimize/fsec-optimize: No such file or directory
   enableParallelBuilding = false;
 
+  passthru.tests = nixosTests.firejail;
+
   meta = {
     inherit (s) version;
     description = ''Namespace-based sandboxing tool for Linux'';