GFileMonitor test: use g_test_skip() instead of g_print()

This stops it from interfering with structured stdout such as TAP.

Bug: https://bugzilla.gnome.org/show_bug.cgi?id=725981
Reviewed-by: Colin Walters <walters@verbum.org>
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>

gio/tests/file.c

@@ -456,7 +456,7 @@ test_create_delete (gconstpointer d)
    */
   if (!strcmp (G_OBJECT_TYPE_NAME (data->monitor), "GPollFileMonitor"))
     {
-      g_print ("skipping test for this GFileMonitor implementation");
+      g_test_skip ("skipping test for this GFileMonitor implementation");
       goto skip;
     }