Add flo's ssh key to the staging grid root user authorized_keys

This MR adds Flo's public SSH key to the list of keys that allow access to the root account on the staging grid.

morph/grid/testing/public-keys/users.nix

@@ -3,7 +3,7 @@ let
   flo = ["ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIHx7wJQNqKn8jOC4AxySRL2UxidNp7uIK9ad3pMb1ifF flo@fs-la"];
 in
   {
-    "root" = jcalderone;
+    "root" = jcalderone ++ flo;
     inherit jcalderone;
     inherit flo;
   }