Add failing test for #916

[goto-bus-stop]

It also reports this, which doesn't make sense:

Error: interface, union and object types must have a subselection set
   ╭─[0119_nested_subselection_issue_916.graphql:8:17]
   │
 8 │ query Invalid { me { name { reviews { body } } } }
   │                 ────────────────┬───────────────
   │                                 ╰───────────────── `Query.me` is an object type `User` and must select fields
───╯

[goto-bus-stop]

The reason appears to be that the executable::Field's subselection gets emptied during ast -> executable conversion, and validation does not know about this