Fix data stream retrieval in TimeSeriesDataStreamsIT (elastic#125621)

This test had the potential to fail when two consecutive GET data
streams requests would hit two different nodes, where one node already
had the cluster state that contained the new backing index and the other
node didn't yet.

Caused by elastic#122852

Fixes elastic#124987

Author: nielsbauman

muted-tests.yml

@@ -357,9 +357,6 @@ tests:
 - class: org.elasticsearch.packaging.test.BootstrapCheckTests
   method: test10Install
   issue: https://github.com/elastic/elasticsearch/issues/124957
-- class: org.elasticsearch.xpack.ilm.TimeSeriesDataStreamsIT
-  method: testRolloverAction
-  issue: https://github.com/elastic/elasticsearch/issues/124987
 - class: org.elasticsearch.packaging.test.DockerTests
   method: test011SecurityEnabledStatus
   issue: https://github.com/elastic/elasticsearch/issues/124990

x-pack/plugin/ilm/qa/multi-node/src/javaRestTest/java/org/elasticsearch/xpack/ilm/TimeSeriesDataStreamsIT.java

@@ -83,9 +83,6 @@ public void testRolloverAction() throws Exception {
             final var backingIndices = getDataStreamBackingIndexNames(dataStream);
             assertEquals(2, backingIndices.size());
             assertTrue(Boolean.parseBoolean((String) getIndexSettingsAsMap(backingIndices.getLast()).get("index.hidden")));
-        });
-        assertBusy(() -> {
-            final var backingIndices = getDataStreamBackingIndexNames(dataStream);
             assertEquals(PhaseCompleteStep.finalStep("hot").getKey(), getStepKeyForIndex(client(), backingIndices.getFirst()));
         });
     }