Looks like a leaked `Exchange`?

**Build scan:**
https://gradle-enterprise.elastic.co/s/mmrtyhckobkwo/tests/:x-pack:plugin:esql:internalClusterTest/org.elasticsearch.xpack.esql.action.EsqlActionIT/testShowFunctions

**Reproduction line:**
```
./gradlew ':x-pack:plugin:esql:internalClusterTest' --tests "org.elasticsearch.xpack.esql.action.EsqlActionIT.testShowFunctions" -Dtests.seed=8850B71504CB7FA5 -Dtests.locale=ar-EG -Dtests.timezone=Asia/Harbin -Druntime.java=21
```

**Applicable branches:**
main

**Reproduces locally?:**
Didn't try

**Failure history:**
https://gradle-enterprise.elastic.co/scans/tests?tests.container=org.elasticsearch.xpack.esql.action.EsqlActionIT&tests.test=testShowFunctions

**Failure excerpt:**
```
java.lang.AssertionError: Leftover exchanges ExchangeService{sinks=[xDupaxgARhq3e5LBrywuWw:4601], sources=[]} on node node_s0

  at org.junit.Assert.fail(Assert.java:88)
  at org.junit.Assert.assertTrue(Assert.java:41)
  at org.elasticsearch.xpack.esql.action.AbstractEsqlIntegTestCase.lambda$ensureExchangesAreReleased$0(AbstractEsqlIntegTestCase.java:38)
  at org.elasticsearch.test.ESTestCase.assertBusy(ESTestCase.java:1196)
  at org.elasticsearch.test.ESTestCase.assertBusy(ESTestCase.java:1169)
  at org.elasticsearch.xpack.esql.action.AbstractEsqlIntegTestCase.ensureExchangesAreReleased(AbstractEsqlIntegTestCase.java:38)
  at jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103)
  at java.lang.reflect.Method.invoke(Method.java:580)
  at com.carrotsearch.randomizedtesting.RandomizedRunner.invoke(RandomizedRunner.java:1758)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$10.evaluate(RandomizedRunner.java:1004)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.tests.util.TestRuleSetupTeardownChained$1.evaluate(TestRuleSetupTeardownChained.java:48)
  at org.apache.lucene.tests.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:43)
  at org.apache.lucene.tests.util.TestRuleThreadAndTestName$1.evaluate(TestRuleThreadAndTestName.java:45)
  at org.apache.lucene.tests.util.TestRuleIgnoreAfterMaxFailures$1.evaluate(TestRuleIgnoreAfterMaxFailures.java:60)
  at org.apache.lucene.tests.util.TestRuleMarkFailure$1.evaluate(TestRuleMarkFailure.java:44)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$StatementRunner.run(ThreadLeakControl.java:390)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl.forkTimeoutingTask(ThreadLeakControl.java:843)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$3.evaluate(ThreadLeakControl.java:490)
  at com.carrotsearch.randomizedtesting.RandomizedRunner.runSingleTest(RandomizedRunner.java:955)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$5.evaluate(RandomizedRunner.java:840)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$6.evaluate(RandomizedRunner.java:891)
  at com.carrotsearch.randomizedtesting.RandomizedRunner$7.evaluate(RandomizedRunner.java:902)
  at org.apache.lucene.tests.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:43)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.tests.util.TestRuleStoreClassName$1.evaluate(TestRuleStoreClassName.java:38)
  at com.carrotsearch.randomizedtesting.rules.NoShadowingOrOverridesOnMethodsRule$1.evaluate(NoShadowingOrOverridesOnMethodsRule.java:40)
  at com.carrotsearch.randomizedtesting.rules.NoShadowingOrOverridesOnMethodsRule$1.evaluate(NoShadowingOrOverridesOnMethodsRule.java:40)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at org.apache.lucene.tests.util.TestRuleAssertionsRequired$1.evaluate(TestRuleAssertionsRequired.java:53)
  at org.apache.lucene.tests.util.AbstractBeforeAfterRule$1.evaluate(AbstractBeforeAfterRule.java:43)
  at org.apache.lucene.tests.util.TestRuleMarkFailure$1.evaluate(TestRuleMarkFailure.java:44)
  at org.apache.lucene.tests.util.TestRuleIgnoreAfterMaxFailures$1.evaluate(TestRuleIgnoreAfterMaxFailures.java:60)
  at org.apache.lucene.tests.util.TestRuleIgnoreTestSuites$1.evaluate(TestRuleIgnoreTestSuites.java:47)
  at com.carrotsearch.randomizedtesting.rules.StatementAdapter.evaluate(StatementAdapter.java:36)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl$StatementRunner.run(ThreadLeakControl.java:390)
  at com.carrotsearch.randomizedtesting.ThreadLeakControl.lambda$forkTimeoutingTask$0(ThreadLeakControl.java:850)
  at java.lang.Thread.run(Thread.java:1583)

```
x-pack/plugin/esql/src/internalClusterTest/java/org/elasticsearch/xpack/esql/action/EsqlActionIT.java
Doc d = new Doc(i, "tag-" + randomIntBetween(1, 100));
            allDocs.add(d);
            indexRequests.add(
                client().prepareIndex().setIndex(indexName).setId(Integer.toString(i)).setSource(Map.of("val", d.val, "tag", d.tag))
            );
        }
        indexRandom(true, randomBoolean(), indexRequests);
        int limit = randomIntBetween(1, 10);
        String command = "from test_extract_fields | sort val | limit " + limit;
        try (EsqlQueryResponse results = run(command)) {
            logger.info(results);
            
            assertThat(results.columns().size(), equalTo(2));
            assertThat(getValuesList(results), hasSize(Math.min(limit, numDocs)));
            assertThat(results.columns().get(1).name(), equalTo("val"));
            assertThat(results.columns().get(0).name(), equalTo("tag"));
            List<Doc> actualDocs = new ArrayList<>();
            for (int i = 0; i < getValuesList(results).size(); i++) {
                List<Object> values = getValuesList(results).get(i);
                actualDocs.add(new Doc((Long) values.get(1), (String) values.get(0)));
            }
            assertThat(actualDocs, equalTo(allDocs.stream().limit(limit).toList()));
        }
    }
    public void testEvalWithNullAndAvg() {
        EsqlQueryResponse results = run("from test | eval nullsum = count_d + null | stats avg(nullsum)");
        logger.info(results);
        Assert.assertEquals(1, results.columns().size());
        Assert.assertEquals(1, getValuesList(results).size());
        assertEquals("avg(nullsum)", results.columns().get(0).name());