Fix occasional SuggestSearchIT failure (#45330)

Refreshes happening during indexing can result differen segment counts and
slightly skewed term statistics, which in turn has the potential to change
suggestion output slightly. In order to prevent this, disable refresh for the
affected tests.

Closes #43261

Author: Christoph Büscher

server/src/test/java/org/elasticsearch/search/suggest/SuggestSearchIT.java

@@ -775,6 +775,7 @@ public void testEmptyShards() throws IOException, InterruptedException {
         assertAcked(prepareCreate("test").setSettings(Settings.builder()
                 .put(indexSettings())
                 .put(IndexSettings.MAX_SHINGLE_DIFF_SETTING.getKey(), 4)
+                .put("index.refresh_interval", -1)  // prevents occasional scoring glitches due to multi segments
                 .put("index.analysis.analyzer.suggest.tokenizer", "standard")
                 .putList("index.analysis.analyzer.suggest.filter", "lowercase", "shingler")
                 .put("index.analysis.filter.shingler.type", "shingle")