Fix SearchServiceTests not waiting for scroll clear (#111547)

We were not waiting on the response here but assume the scrolls are cleared
in the following lines. This worked as long as the transport action wasn't forking but is broken now
that we fork to generic. Fixed by just waiting.

closes #111529

Author: original-brownbear

server/src/test/java/org/elasticsearch/search/SearchServiceTests.java

@@ -1548,7 +1548,7 @@ public void testMaxOpenScrollContexts() throws Exception {
 
         ClearScrollRequest clearScrollRequest = new ClearScrollRequest();
         clearScrollRequest.setScrollIds(clearScrollIds);
-        client().clearScroll(clearScrollRequest);
+        client().clearScroll(clearScrollRequest).get();
 
         for (int i = 0; i < clearScrollIds.size(); i++) {
             client().prepareSearch("index").setSize(1).setScroll(TimeValue.timeValueMinutes(1)).get().decRef();