Fix problem in filenotify-tests

* lisp/net/tramp-sh.el (tramp-sh-handle-file-notify-add-watch):
Adapt `accept-process-output' argument.

* test/lisp/filenotify-tests.el (file-notify--deftest-remote):
Remove :unstable tag.

lisp/net/tramp-sh.el

@@ -3647,7 +3647,7 @@ Fall back to normal file name handler if no Tramp handler exists."
 	(set-process-filter p filter)
 	;; There might be an error if the monitor is not supported.
 	;; Give the filter a chance to read the output.
-	(while (tramp-accept-process-output p))
+	(while (tramp-accept-process-output p 0))
 	(unless (process-live-p p)
 	  (tramp-error
 	   p 'file-notify-error "Monitoring not supported for `%s'" file-name))

test/lisp/filenotify-tests.el

@@ -266,7 +266,7 @@ This returns only for the local case and gfilenotify; otherwise it is nil.
   (declare (indent 1))
   `(ert-deftest ,(intern (concat (symbol-name test) "-remote")) ()
      ,docstring
-     :tags '(:expensive-test :unstable)
+     :tags '(:expensive-test)
      :expected-result (or ,expected :passed)
      (skip-unless (not ,skip))
      (let* ((temporary-file-directory