Add index mode feature flag to data stream's test task. (elastic#86348)

Closes elastic#86333

Author: martijnvg

modules/data-streams/build.gradle

@@ -49,4 +49,7 @@ if (BuildParams.isSnapshotBuild() == false) {
   tasks.named("internalClusterTest").configure {
     systemProperty 'es.index_mode_feature_flag_registered', 'true'
   }
+  tasks.named("test").configure {
+    systemProperty 'es.index_mode_feature_flag_registered', 'true'
+  }
 }

modules/data-streams/src/test/java/org/elasticsearch/datastreams/MetadataIndexTemplateServiceTests.java

@@ -46,7 +46,6 @@
  */
 public class MetadataIndexTemplateServiceTests extends ESSingleNodeTestCase {
 
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/86333")
     public void testValidateTsdbDataStreamsReferringTsdbTemplate() throws Exception {
         var state = ClusterState.EMPTY_STATE;
         final var service = getMetadataIndexTemplateService();