wasabibackend: add update script

pkgs/by-name/wa/wasabibackend/package.nix

@@ -6,6 +6,7 @@
   dotnetCorePackages,
   zlib,
   openssl,
+  nix-update-script,
   nixosTests,
 }:
 buildDotnetModule rec {
@@ -45,9 +46,12 @@ buildDotnetModule rec {
     mv $out/bin/WalletWasabi.Backend $out/bin/WasabiBackend
   '';
 
-  passthru.tests = {
+  passthru = {
+    updateScript = nix-update-script { };
+    tests = {
       inherit (nixosTests) wasabibackend;
     };
+  };
 
   meta = {
     description = "Backend for the Wasabi Wallet";