### CI Link

https://gradle-enterprise.elastic.co/s/opv3672lmdhmi

### Repro line

./gradlew ':x-pack:plugin:autoscaling:internalClusterTest' --tests "org.elasticsearch.xpack.autoscaling.storage.ReactiveStorageIT.testScaleWhileShrinking" -Dtests.seed=F89DAF53966040FE -Dtests.locale=ar-BH -Dtests.timezone=Europe/Gibraltar -Druntime.java=19

### Does it reproduce?

No

### Applicable branches

main

### Failure history

https://gradle-enterprise.elastic.co/scans/tests?search.timeZoneId=Europe/Rome&tests.container=org.elasticsearch.xpack.autoscaling.storage.ReactiveStorageIT&tests.test=testScaleWhileShrinking

### Failure excerpt

```
java.lang.NullPointerException: Cannot invoke "org.elasticsearch.cluster.DiskUsage.getFreeBytes()" because the return value of "java.util.Map.get(Object)" is null
```

It looks like method `getNodeMostAvailableDiskUsages` returns a null value which results in a NPE when calling get on the expected result map.
x-pack/plugin/autoscaling/src/internalClusterTest/java/org/elasticsearch/xpack/autoscaling/storage/ReactiveStorageIT.java
waitForRelocation();
        
        
        
        
        assertBusy(() -> {
            refreshClusterInfo();
            final ClusterInfo clusterInfo = getClusterInfo();
            final long freeBytes = clusterInfo.getNodeMostAvailableDiskUsages().get(dataNode2Id).getFreeBytes();
            assertThat(freeBytes, is(equalTo(enoughSpaceForColocation)));
        });
        String shrinkName = "shrink-" + indexName;
        assertAcked(
            client().admin()
                .indices()
                .prepareResizeIndex(indexName, shrinkName)
                .setSettings(
                    Settings.builder()
                        .put(IndexMetadata.SETTING_NUMBER_OF_SHARDS, 1)
                        .put(IndexMetadata.SETTING_NUMBER_OF_REPLICAS, 0)
                        .build()
                )
                .setWaitForActiveShards(ActiveShardCount.NONE)
                .get()
        );
        
        long requiredSpaceForShrink = used * 2 + LOW_WATERMARK_BYTES;
        response = capacity();
        assertThat(response.results().keySet(), equalTo(Set.of(policyName)));
        assertThat(