### CI Link

https://gradle-enterprise.elastic.co/s/yp56iltyyinha

### Repro line

./gradlew ':x-pack:plugin:ilm:qa:multi-node:javaRestTest' --tests "org.elasticsearch.xpack.ilm.ChangePolicyforIndexIT.testChangePolicyForIndex" -Dtests.seed=8825024EAE3089DD -Dtests.locale=en-PH -Dtests.timezone=Asia/Karachi -Druntime.java=16

### Does it reproduce?

No

### Applicable branches

7.17 (probably all 8+)

### Failure history

_No response_

### Failure excerpt

This is rather concerning
```
java.lang.AssertionError: policy step registry cache failed sanity check
	at org.elasticsearch.xpack.ilm.PolicyStepsRegistry.getStep(PolicyStepsRegistry.java:378) ~[?:?]
	at org.elasticsearch.xpack.ilm.IndexLifecycleRunner.getCurrentStep(IndexLifecycleRunner.java:108) ~[?:?]
	at org.elasticsearch.xpack.ilm.IndexLifecycleRunner.runPolicyAfterStateChange(IndexLifecycleRunner.java:430) ~[?:?]
	at org.elasticsearch.xpack.ilm.IndexLifecycleService.triggerPolicies(IndexLifecycleService.java:416) ~[?:?]
	at org.elasticsearch.xpack.ilm.IndexLifecycleService.clusterChanged(IndexLifecycleService.java:319) ~[?:?]
	at org.elasticsearch.cluster.service.ClusterApplierService.callClusterStateListener(ClusterApplierService.java:573) ~[elasticsearch-7.17.2-SNAPSHOT.jar:7.17.2-SNAPSHOT]
	at org.elasticsearch.cluster.service.ClusterApplierService.callClusterStateListeners(ClusterApplierService.java:559) ~[elasticsearch-7.17.2-SNAPSHOT.jar:7.17.2-SNAPSHOT]
	at org.elasticsearch.cluster.service.ClusterApplierService.applyChanges(ClusterApplierService.java:519) ~[elasticsearch-7.17.2-SNAPSHOT.jar:7.17.2-SNAPSHOT]
	at org.elasticsearch.cluster.service.ClusterApplierService.runTask(ClusterApplierService.java:428) ~[elasticsearch-7.17.2-SNAPSHOT.jar:7.17.2-SNAPSHOT]
	at org.elasticsearch.cluster.service.ClusterApplierService.access$000(ClusterApplierService.java:56) ~[elasticsearch-7.17.2-SNAPSHOT.jar:7.17.2-SNAPSHOT]
	at org.elasticsearch.cluster.service.ClusterApplierService$UpdateTask.run(ClusterApplierService.java:154) ~[elasticsearch-7.17.2-SNAPSHOT.jar:7.17.2-SNAPSHOT]
	at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingRunnable.run(ThreadContext.java:718) ~[elasticsearch-7.17.2-SNAPSHOT.jar:7.17.2-SNAPSHOT]
	at org.elasticsearch.common.util.concurrent.PrioritizedEsThreadPoolExecutor$TieBreakingPrioritizedRunnable.runAndClean(PrioritizedEsThreadPoolExecutor.java:262) ~[elasticsearch-7.17.2-SNAPSHOT.jar:7.17.2-SNAPSHOT]
	at org.elasticsearch.common.util.concurrent.PrioritizedEsThreadPoolExecutor$TieBreakingPrioritizedRunnable.run(PrioritizedEsThreadPoolExecutor.java:225) ~[elasticsearch-7.17.2-SNAPSHOT.jar:7.17.2-SNAPSHOT]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130) ~[?:?]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630) ~[?:?]
	at java.lang.Thread.run(Thread.java:831) [?:?]
[2022-03-15T09:34:09.657115416Z] [BUILD] Stopping node
```
x-pack/plugin/ilm/src/test/java/org/elasticsearch/xpack/ilm/PolicyStepsRegistryTests.java
/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0; you may not use this file except in compliance with the Elastic License
 * 2.0.
 */
package org.elasticsearch.xpack.ilm;
import org.elasticsearch.Version;
import org.elasticsearch.client.internal.Client;
import org.elasticsearch.cluster.ClusterName;
import org.elasticsearch.cluster.ClusterState;
import org.elasticsearch.cluster.metadata.IndexMetadata;
import org.elasticsearch.cluster.metadata.LifecycleExecutionState;
import org.elasticsearch.cluster.metadata.Metadata;
import org.elasticsearch.cluster.node.DiscoveryNode;
import org.elasticsearch.cluster.node.DiscoveryNodes;
import org.elasticsearch.common.Strings;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.transport.TransportAddress;
import org.elasticsearch.core.TimeValue;
import org.elasticsearch.index.Index;
import org.elasticsearch.test.ESTestCase;
import org.elasticsearch.test.NodeRoles;
import org.elasticsearch.xcontent.NamedXContentRegistry;
import org.elasticsearch.xcontent.ToXContent;
import org.elasticsearch.xcontent.XContentBuilder;