Fix find-dired-with-command for remote directories

* lisp/find-dired.el (find-dired-with-command):
Use `start-file-process-shell-command'.  (Bug#64897)

lisp/find-dired.el

@@ -244,8 +244,8 @@ it finishes, type \\[kill-find]."
     (erase-buffer)
     (setq default-directory dir)
     ;; Start the find process.
-    (shell-command (concat command "&") (current-buffer))
-    (let ((proc (get-buffer-process (current-buffer))))
+    (let ((proc (start-file-process-shell-command
+                 (buffer-name) (current-buffer) command)))
       ;; Initialize the process marker; it is used by the filter.
       (move-marker (process-mark proc) (point) (current-buffer))
       (set-process-filter proc #'find-dired-filter)