Fix testIdenticalSearchableSnapshotActionIsNoop (#69033)

This fixes the flakiness in testIdenticalSearchableSnapshotActionIsNoop and
testConvertingSearchableSnapshotFromFullToPartial caused by the fact that we
enabled ILM for the index and *after that* indexed a document. If ILM runs
very fast in CI the `indexDocument` call could fail, or in the case of
testIdenticalSearchableSnapshotActionIsNoop all the assertions in the test
will pass but the final one that checks there is one document indexed fails
because the `indexDocument` call didn't execute.

x-pack/plugin/ilm/qa/multi-node/src/javaRestTest/java/org/elasticsearch/xpack/ilm/actions/SearchableSnapshotActionIT.java

@@ -375,12 +375,14 @@ public class SearchableSnapshotActionIT extends ESRestTestCase {
             null
         );
 
-        createIndex(index, Settings.builder()
-            .put(LifecycleSettings.LIFECYCLE_NAME, policy)
-            .build());
+        createIndex(index, Settings.EMPTY);
         ensureGreen(index);
         indexDocument(client(), index, true);
 
+        // enable ILM after we indexed a document as otherwise ILM might sometimes run so fast the indexDocument call will fail with
+        // `index_not_found_exception`
+        updateIndexSettings(index, Settings.builder().put(LifecycleSettings.LIFECYCLE_NAME, policy));
+
         final String searchableSnapMountedIndexName = (storage == MountSearchableSnapshotRequest.Storage.FULL_COPY ?
             SearchableSnapshotAction.FULL_RESTORED_INDEX_PREFIX : SearchableSnapshotAction.PARTIAL_RESTORED_INDEX_PREFIX) + index;
 
@@ -425,12 +427,14 @@ public class SearchableSnapshotActionIT extends ESRestTestCase {
             null
         );
 
-        createIndex(index, Settings.builder()
-            .put(LifecycleSettings.LIFECYCLE_NAME, policy)
-            .build());
+        createIndex(index, Settings.EMPTY);
         ensureGreen(index);
         indexDocument(client(), index, true);
 
+        // enable ILM after we indexed a document as otherwise ILM might sometimes run so fast the indexDocument call will fail with
+        // `index_not_found_exception`
+        updateIndexSettings(index, Settings.builder().put(LifecycleSettings.LIFECYCLE_NAME, policy));
+
         final String searchableSnapMountedIndexName = SearchableSnapshotAction.PARTIAL_RESTORED_INDEX_PREFIX +
             SearchableSnapshotAction.FULL_RESTORED_INDEX_PREFIX + index;