Fix testRunStateChangePolicyWithAsyncActionNextStep race condition (#40707)

Previously we only set the latch countdown with `nextStep.setLatch` after the
cluster state change has already been counted down. However, it's possible
execution could have already started, causing the latch to be missed when the
`MockAsyncActionStep` is being executed.

This moves the latch setting to be before the call to
`runPolicyAfterStateChange`, which means it is always available when the
`MockAsyncActionStep` is executed.

I was able to reproduce the failure every 30-40 runs before this change. With
this change, running 2000+ times the test passes.

Resolves #40018

Author: dakrone

x-pack/plugin/ilm/src/test/java/org/elasticsearch/xpack/indexlifecycle/IndexLifecycleRunnerTests.java

@@ -385,14 +385,12 @@ public void testRunStateChangePolicyWithAsyncActionNextStep() throws Exception {
         ClusterState before = clusterService.state();
         CountDownLatch latch = new CountDownLatch(1);
         step.setLatch(latch);
+        CountDownLatch asyncLatch = new CountDownLatch(1);
+        nextStep.setLatch(asyncLatch);
         runner.runPolicyAfterStateChange(policyName, indexMetaData);
 
         // Wait for the cluster state action step
         awaitLatch(latch, 5, TimeUnit.SECONDS);
-
-        CountDownLatch asyncLatch = new CountDownLatch(1);
-        nextStep.setLatch(asyncLatch);
-
         // Wait for the async action step
         awaitLatch(asyncLatch, 5, TimeUnit.SECONDS);
         ClusterState after = clusterService.state();