nixos/pretix: raise TimeoutStartSec

On some slower systems or ones with a slower database (connection) the
initial migrations can exceed the default 90s timeout.

nixos/modules/services/web-apps/pretix.nix

@@ -535,6 +535,7 @@ in
           fi
         '';
         serviceConfig = {
+          TimeoutStartSec = "5min";
           ExecStart = "${getExe' pythonEnv "gunicorn"} --bind unix:/run/pretix/pretix.sock ${cfg.gunicorn.extraArgs} pretix.wsgi";
           RuntimeDirectory = "pretix";
         };