[7.13] Fix SearchableSnapshotActionIT.testConvertingSearchableSnapshotFromFullToPartial (#73994)

This failure can happen if the after test logic in 
EsRestTestCase.wipeSearchableSnapshotsIndices() 
correctly found a searchable snapshot index to 
delete but that index was already deleted and 
converted to an alias in the meanwhile, by the 
last step of the ILM searchable snapshot action 
for frozen phase.

This in-flight alias swap while the partially index 
has a completed ILM state is possible because 
of the CopyExecutionStateStep which updates 
the cluster state with completed in frozen phase 
and the alias swap request is executed after the 
updated cluster state is published.

Backport of #73888
Closes #73706

Author: tlrx

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ilm/CopyExecutionStateStep.java

@@ -78,7 +78,6 @@ public ClusterState performAction(Index index, ClusterState clusterState) {
         String phase = targetNextStepKey.getPhase();
         String action = targetNextStepKey.getAction();
         String step = targetNextStepKey.getName();
-        long lifecycleDate = lifecycleState.getLifecycleDate();
 
         LifecycleExecutionState.Builder relevantTargetCustomData = LifecycleExecutionState.builder(lifecycleState);
         // Override the phase, action, and step for the target next StepKey

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

@@ -453,6 +453,11 @@ public void testConvertingSearchableSnapshotFromFullToPartial() throws Exception
         Request hitCount = new Request("GET", "/" + searchableSnapMountedIndexName + "/_count");
         Map<String, Object> count = entityAsMap(client().performRequest(hitCount));
         assertThat("expected a single document but got: " + count, (int) count.get("count"), equalTo(1));
+
+        assertBusy(() -> assertTrue(
+            "Expecting the mounted index to be deleted and to be converted to an alias",
+            aliasExists(searchableSnapMountedIndexName, SearchableSnapshotAction.FULL_RESTORED_INDEX_PREFIX + index))
+        );
     }
 
     public void testSecondSearchableSnapshotUsingDifferentRepoThrows() throws Exception {