ocaml: Fix guestfs_065_implicit_close.ml for OCaml 5

Link: https://discuss.ocaml.org/t/ocaml-5-forcing-objects-to-be-collected-and-finalized/12492/3
Thanks: Josh Berdine
Thanks: Vincent Laviron

ocaml/t/guestfs_065_implicit_close.ml

@@ -16,10 +16,12 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  *)
 
-let close_invoked = ref 0
+let [@inline never][@local never] run () =
+  let close_invoked = ref 0 in
 
   let close _ _ _ _ =
     incr close_invoked
+  in
 
   let () =
     let g = new Guestfs.guestfs () in
@@ -28,10 +30,13 @@ let () =
   (* Allow the 'g' handle to go out of scope here, to ensure there is no
    * reference held on the stack.
    *)
+  in
 
   (* This should cause the GC to close the handle. *)
-let () = Gc.full_major ()
+  Gc.full_major ();
 
-let () = assert  (!close_invoked = 1)
+  assert  (!close_invoked = 1);
 
-let () = Gc.compact ()
+  Gc.compact ()
+
+let () = run ()