step-ca: re-enable tests on darwin by enabling local networking

pkgs/tools/security/step-ca/default.nix

@@ -42,10 +42,9 @@ buildGoModule rec {
     install -Dm444 -t $out/lib/systemd/system systemd/step-ca.service
   '';
 
-  # Tests fail on darwin with
-  # panic: httptest: failed to listen on a port: listen tcp6 [::1]:0: bind: operation not permitted [recovered]
-  # probably some sandboxing issue
-  doCheck = stdenv.isLinux;
+  # Tests start http servers which need to bind to local addresses:
+  # panic: httptest: failed to listen on a port: listen tcp6 [::1]:0: bind: operation not permitted
+  __darwinAllowLocalNetworking = true;
 
   meta = with lib; {
     description = "A private certificate authority (X.509 & SSH) & ACME server for secure automated certificate management, so you can use TLS everywhere & SSO for SSH";