[7.x] Fix SearchableSnapshotsPersistentCacheIntegTests.testPersistentCacheCleanUpAfterRelocation

On 7.x the test should always use soft deletes because
peer recovery always copies .liv files but searchable
snapshot directories do not support writing files.

Relates elastic#55142
Closes elastic#72857

Author: tlrx

x-pack/plugin/searchable-snapshots/src/internalClusterTest/java/org/elasticsearch/xpack/searchablesnapshots/cache/full/SearchableSnapshotsPersistentCacheIntegTests.java

@@ -162,7 +162,6 @@ public Settings onNodeStopped(String nodeName) {
         });
     }
 
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/72857")
     public void testPersistentCacheCleanUpAfterRelocation() throws Exception {
         internalCluster().startMasterOnlyNode();
         internalCluster().ensureAtLeastNumDataNodes(3);
@@ -179,6 +178,7 @@ public void testPersistentCacheCleanUpAfterRelocation() throws Exception {
             Settings.builder()
                 .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 3)
                 .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, randomIntBetween(0, 1))
+                .put(INDEX_SOFT_DELETES_SETTING.getKey(), true)
         );
 
         final String snapshotName = prefix + "snapshot";
@@ -190,6 +190,7 @@ public void testPersistentCacheCleanUpAfterRelocation() throws Exception {
 
         assertExecutorIsIdle(SearchableSnapshotsConstants.CACHE_FETCH_ASYNC_THREAD_POOL_NAME);
         assertExecutorIsIdle(SearchableSnapshotsConstants.CACHE_PREWARMING_THREAD_POOL_NAME);
+        waitForRelocation();
 
         RecoveryResponse recoveryResponse = client().admin().indices().prepareRecoveries(mountedIndexName).get();
         assertTrue(recoveryResponse.shardRecoveryStates().containsKey(mountedIndexName));