added sleep call to wait for index finish

Author: rtschu

tests/search_test.php

@@ -45,6 +45,7 @@ public function test_discussion_discussion() {
 
         [$discussion, $post1] = $moodleoverflowgen->post_to_forum($moodleoverflow, $user);
         $post2 = $moodleoverflowgen->post_to_discussion($moodleoverflow, $discussion, $user);
+        $this->waitForSecond();
 
         $searchmanager = \core_search\manager::instance();
         $searchmanager->index(true);