Fix test

Author: gmarouli

server/src/test/java/org/elasticsearch/action/datastreams/lifecycle/ExplainDataStreamLifecycleResponseTests.java

@@ -311,7 +311,7 @@ private Response randomResponse() {
         );
         var failuresGlobalRetention = DataStreamGlobalRetention.create(
             randomBoolean() ? TimeValue.timeValueDays(randomIntBetween(1, 10)) : null,
-            dataGlobalRetention.maxRetention()
+            dataGlobalRetention == null ? null : dataGlobalRetention.maxRetention()
         );
         return new Response(
             List.of(