Fix inference test

ocaml/testsuite/tests/typing-layouts/jkinds.ml

@@ -1664,5 +1664,16 @@ Error: The layout of type t is value, because
        But the layout of type t must be a sublayout of value, because
          of the annotation on the declaration of the type t.
 |}]
+
+type 'a t : value mod many = { x : 'a }
+[%%expect {|
+Line 1, characters 0-39:
+1 | type 'a t : value mod many = { x : 'a }
+    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+Error: The layout of type t is value, because
+         it's a boxed record type.
+       But the layout of type t must be a sublayout of value, because
+         of the annotation on the declaration of the type t.
+|}]
 (* CR layouts v2.8: this should be accepted; 'a should be inferred to have kind
-  value mod global *)
+  value mod many *)