Fix random sampler consistency test (#107957)

Random sampler consistency requires a restricted number of segments, to
ensure we always hit the same number of segments and that no merging is
occurring, this merges the segment count to 1 for this particular test. 

In practice, this isn't needed as the approximate nature of the
aggregation already means you could get different statistics per call,
but they are within an error bound set by the users configured sampling
probability.

closes: #105839

server/src/internalClusterTest/java/org/elasticsearch/search/aggregations/bucket/RandomSamplerIT.java

@@ -22,6 +22,7 @@
 
 import static org.elasticsearch.search.aggregations.AggregationBuilders.avg;
 import static org.elasticsearch.search.aggregations.AggregationBuilders.histogram;
+import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertNoFailures;
 import static org.elasticsearch.test.hamcrest.ElasticsearchAssertions.assertResponse;
 import static org.elasticsearch.xcontent.XContentFactory.jsonBuilder;
 import static org.hamcrest.Matchers.equalTo;
@@ -83,9 +84,11 @@ public void setupSuiteScopeCluster() throws Exception {
         }
         indexRandom(true, builders);
         ensureSearchable();
+        // Force merge to ensure segment consistency as any segment merging can change which particular documents
+        // are sampled
+        assertNoFailures(indicesAdmin().prepareForceMerge("idx").setMaxNumSegments(1).get());
     }
 
-    @AwaitsFix(bugUrl = "https://github.com/elastic/elasticsearch/issues/105839")
     public void testRandomSamplerConsistentSeed() {
         double[] sampleMonotonicValue = new double[1];
         double[] sampleNumericValue = new double[1];