Do not always close stdout in [run_in_directory]

This fixes the ppx test

ocaml-lsp-server/src/ocaml_lsp_server.ml

@@ -879,7 +879,7 @@ let run_in_directory ~prog ~prog_is_quoted:_ ~args ~cwd ?stdin:_ ?stdout
   let prog = "/bin/sh" in
   let argv = [ "sh"; "-c"; cmd ] in
   let stdin = Unix.openfile "/dev/null" [ Unix.O_RDONLY ] 0x777 in
-  let stdout =
+  let out =
     match stdout with
     | Some file -> Unix.openfile file [ Unix.O_WRONLY ] 0x664
     | None ->
@@ -889,7 +889,7 @@ let run_in_directory ~prog ~prog_is_quoted:_ ~args ~cwd ?stdin:_ ?stdout
   in
   let pid =
     let cwd : Spawn.Working_dir.t = Path cwd in
-    Spawn.spawn ~cwd ~prog ~argv ~stdin ~stdout ()
+    Spawn.spawn ~cwd ~prog ~argv ~stdin ~stdout:out ()
   in
   let _, status = Unix.waitpid [] pid in
   let res =
@@ -899,7 +899,7 @@ let run_in_directory ~prog ~prog_is_quoted:_ ~args ~cwd ?stdin:_ ?stdout
     | WSTOPPED _ -> -1
   in
   Unix.close stdin;
-  Unix.close stdout;
+  if Option.is_some stdout then Unix.close out;
   `Finished res
 
 let run_in_directory =

ocaml-lsp-server/test/e2e-new/with_ppx.ml

@@ -86,5 +86,14 @@ let%expect_test "with-ppx" =
   print_endline !output;
   [%expect {|
     Received 0 diagnostics
-    no hover response|}]
+    {
+      "contents": {
+        "kind": "plaintext",
+        "value": "Expect_test_common.File.Location.t"
+      },
+      "range": {
+        "end": { "character": 8, "line": 97 },
+        "start": { "character": 2, "line": 86 }
+      }
+    }|}]