spire: add nixos tests to passthru

pkgs/by-name/sp/spire/package.nix

@@ -2,6 +2,7 @@
   lib,
   buildGoModule,
   fetchFromGitHub,
+  nixosTests,
   openssl,
 }:
 
@@ -85,6 +86,10 @@ buildGoModule (finalAttrs: {
     runHook postInstallCheck
   '';
 
+  passthru.tests = {
+    inherit (nixosTests) spire;
+  };
+
   meta = {
     description = "SPIFFE Runtime Environment";
     homepage = "https://spiffe.io/";