nixos/tests: fix nginx-pubhtml test

nixos/tests/nginx-pubhtml.nix

@@ -2,6 +2,7 @@ import ./make-test-python.nix {
   name = "nginx-pubhtml";
 
   machine = { pkgs, ... }: {
+    systemd.services.nginx.serviceConfig.ProtectHome = "read-only";
     services.nginx.enable = true;
     services.nginx.virtualHosts.localhost = {
       locations."~ ^/\\~([a-z0-9_]+)(/.*)?$".alias = "/home/$1/public_html$2";