### 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/main/java/org/elasticsearch/xpack/ilm/PolicyStepsRegistry.java
} else {
            return steps.containsKey(stepKey);
        }
    }
    public boolean policyExists(final String policy) {
        return lifecyclePolicyMap.containsKey(policy);
    }
    public Step getFirstStep(String policy) {
        return firstStepMap.get(policy);
    }
    public TimeValue getIndexAgeForPhase(final String policy, final String phase) {
        
        if (InitializePolicyContextStep.INITIALIZATION_PHASE.equals(phase) || TerminalPolicyStep.COMPLETED_PHASE.equals(phase)) {
            return TimeValue.ZERO;
        }
        final LifecyclePolicyMetadata meta = lifecyclePolicyMap.get(policy);
        if (meta == null) {
            throw new IllegalArgumentException("no policy found with name \"" + policy + "\"");
        } else {
            final Phase retrievedPhase = meta.getPolicy().getPhases().get(phase);
            if (retrievedPhase == null) {
                
                return TimeValue.ZERO;
            } else {
                return retrievedPhase.getMinimumAge();
            }
        }
    }
}