Fix DataStreamLifecycleDownsampleIT.testUpdateDownsampleSamplingMode (#138174)

It was clear from failed tests that DLM was still progressing when the
timeout of 10s was reached. Since DLM works on a poll interval (set to
1s in these tests), there's not much we can do to speed up the test.
Therefore, we simply bump the timeout from 10s to 30s. This should give
DLM enough time to complete the downsampling mode change.

Note that `safeAwait` uses a timeout of 10s and `awaitClusterState` uses
a timeout of 30s; that's why there's no explicit timeout change.

Fixes #138135

Author: nielsbauman

muted-tests.yml

@@ -453,9 +453,6 @@ tests:
 - class: org.elasticsearch.upgrades.IndexSortUpgradeIT
   method: testIndexSortForNumericTypes {upgradedNodes=1}
   issue: https://github.com/elastic/elasticsearch/issues/138130
-- class: org.elasticsearch.xpack.downsample.DataStreamLifecycleDownsampleIT
-  method: testUpdateDownsampleSamplingMode
-  issue: https://github.com/elastic/elasticsearch/issues/138135
 - class: org.elasticsearch.xpack.inference.integration.CCMServiceIT
   method: testCreatesEisChatCompletionEndpoint
   issue: https://github.com/elastic/elasticsearch/issues/138206

x-pack/plugin/downsample/src/internalClusterTest/java/org/elasticsearch/xpack/downsample/DataStreamLifecycleDownsampleIT.java

@@ -21,7 +21,6 @@
 import org.elasticsearch.core.TimeValue;
 import org.elasticsearch.datastreams.lifecycle.DataStreamLifecycleService;
 import org.elasticsearch.search.aggregations.bucket.histogram.DateHistogramInterval;
-import org.elasticsearch.test.ClusterServiceUtils;
 import org.elasticsearch.test.junit.annotations.TestLogging;
 
 import java.util.HashSet;
@@ -352,17 +351,15 @@ public void testUpdateDownsampleSamplingMode() throws Exception {
         rolloverResponse = safeGet(client().execute(RolloverAction.INSTANCE, new RolloverRequest(dataStreamName, null)));
         assertTrue(rolloverResponse.isRolledOver());
         String downsampledPrefix = "downsample-10m-";
-        final var waitForUpdatedDownsamplingRound = ClusterServiceUtils.addMasterTemporaryStateListener(clusterState -> {
+        awaitClusterState(clusterState -> {
             ProjectMetadata projectMetadata = clusterState.metadata().getProject();
             final var dataStream = projectMetadata.dataStreams().get(dataStreamName);
             if (dataStream == null) {
                 return false;
             }
-
             return dataStream.getIndices().size() > 2
                 && dataStream.getIndices().stream().filter(index -> index.getName().startsWith(downsampledPrefix)).count() == 2;
         });
-        safeAwait(waitForUpdatedDownsamplingRound);
         assertDownsamplingMethod(initialSamplingMethod, downsampledPrefix + firstBackingIndex);
         assertDownsamplingMethod(updatedSamplingMethod, downsampledPrefix + secondBackingIndex);
     }