castxml: use testers.testVersion in passthru.tests

(in order to prevent CLI regressions such as https://github.com/NixOS/nixpkgs/pull/318055)

pkgs/by-name/ca/castxml/package.nix

@@ -7,6 +7,7 @@
   llvmPackages,
   python3,
   stdenv,
+  testers,
   zlib,
   # Boolean flags
   withHTML ? true,
@@ -66,6 +67,10 @@ stdenv.mkDerivation (finalAttrs: {
     runHook postCheck
   '';
 
+  passthru.tests = testers.testVersion {
+    package = finalAttrs.finalPackage;
+  };
+
   meta = {
     homepage = "https://github.com/CastXML/CastXML";
     description = "C-family Abstract Syntax Tree XML Output";