soupault: add version test

pkgs/tools/typesetting/soupault/default.nix

@@ -1,6 +1,8 @@
 { lib
 , fetchFromGitea
 , ocamlPackages
+, soupault
+, testers
 }:
 
 ocamlPackages.buildDunePackage rec {
@@ -37,6 +39,11 @@ ocamlPackages.buildDunePackage rec {
     yaml
   ];
 
+  passthru.tests.version = testers.testVersion {
+    package = soupault;
+    command = "soupault --version-number";
+  };
+
   meta = {
     description = "A tool that helps you create and manage static websites";
     homepage = "https://soupault.app/";