fix: don't autostart CaT VPN

This was just failing on autostart, often because the network was not
available yet.

users/ben/concepts-and-training.nix

@@ -22,6 +22,7 @@ in {
 
   services.openvpn.servers = {
     catVPN = {
+      autoStart = false;
       config = ''config ${config.age.secrets."cat-test.ovpn".path}'';
     };
   };