Extra blank lines with OCaml 5.1 (alpha)

[talex5]

Some of the Eio MDX tests were failing with OCaml 5.1 due to extra blank lines appearing in the output. It seems to be related to hidden deprecation warnings. Here's a simple test-case:

```ocaml
module F : sig
  val x : unit [@@ocaml.deprecated "Hmm"]
end = struct
  let x = ()
end

let x = F.x
```

```ocaml
# print_endline "foo";;
- : unit = ()
```

With OCaml 5.0, this produces:

# print_endline "foo";;
foo
- : unit = ()

But with 5.1 we get an extra blank line:

# print_endline "foo";;
foo

- : unit = ()