[Test] Fix WriteLoadForecasterIT testWriteLoadForecastIsOverriddenBySetting (#134099)

Ensure green after rollover to avoid unexpected license state flipping.

Resolves: #133455

x-pack/plugin/write-load-forecaster/src/internalClusterTest/java/org/elasticsearch/xpack/writeloadforecaster/WriteLoadForecasterIT.java

@@ -194,6 +194,7 @@ public class WriteLoadForecasterIT extends ESIntegTestCase {
 
             assertAcked(indicesAdmin().rolloverIndex(new RolloverRequest(dataStreamName, null)).actionGet());
         }
+        ensureGreen();
     }
 
     static void indexDocs(String dataStream, int numDocs) {