### CI Link

https://gradle-enterprise.elastic.co/s/yckwl5zjomfas

### Repro line

```
./gradlew ':server:test' --tests "org.elasticsearch.cluster.coordination.CoordinatorTests.testSingleNodeDiscoveryStabilisesEvenWhenDisrupted" -Dtests.seed=949AB28501F8ED37:BBC20DD1A5D4EF81
```

### Does it reproduce?

Yes

### Applicable branches

main

### Failure history

https://ci-stats.elastic.co/s/jenkins/goto/da1547f0-2ea6-11ed-8233-4bd40c8511bb - 3 similar-looking failures over the last 90 days

### Failure excerpt

```org.elasticsearch.cluster.coordination.CoordinatorTests > testSingleNodeDiscoveryStabilisesEvenWhenDisrupted FAILED
    java.lang.AssertionError: leaders
    Expected: not an empty collection
         but: was <[]>
        at __randomizedtesting.SeedInfo.seed([949AB28501F8ED37:BBC20DD1A5D4EF81]:0)
        at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18)
        at org.junit.Assert.assertThat(Assert.java:956)
        at org.elasticsearch.cluster.coordination.AbstractCoordinatorTestCase$Cluster.getAnyLeader(AbstractCoordinatorTestCase.java:791)
        at org.elasticsearch.cluster.coordination.CoordinatorTests.testSingleNodeDiscoveryStabilisesEvenWhenDisrupted(CoordinatorTests.java:1939)


Suite: Test class org.elasticsearch.cluster.coordination.CoordinatorTests
  2> REPRODUCE WITH: ./gradlew ':server:test' --tests "org.elasticsearch.cluster.coordination.CoordinatorTests.testSingleNodeDiscoveryStabilisesEvenWhenDisrupted" -Dtests.seed=949AB28501F8ED37 -Dtests.locale=en-AU -Dtests.timezone=Europe/Vienna -Druntime.java=18
  2> java.lang.AssertionError: leaders
    Expected: not an empty collection
         but: was <[]>
        at __randomizedtesting.SeedInfo.seed([949AB28501F8ED37:BBC20DD1A5D4EF81]:0)
        at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18)
        at org.junit.Assert.assertThat(Assert.java:956)
        at org.elasticsearch.cluster.coordination.AbstractCoordinatorTestCase$Cluster.getAnyLeader(AbstractCoordinatorTestCase.java:791)
        at org.elasticsearch.cluster.coordination.CoordinatorTests.testSingleNodeDiscoveryStabilisesEvenWhenDisrupted(CoordinatorTests.java:1939)
  2> NOTE: leaving temporary files on disk at: /home/davidturner/src/elasticsearch/server/build/testrun/test/temp/org.elasticsearch.cluster.coordination.CoordinatorTests_949AB28501F8ED37-002
  2> NOTE: test params are: codec=Asserting(Lucene94): {}, docValues:{}, maxPointsInLeafNode=1598, maxMBSortInHeap=6.485414969465074, sim=Asserting(RandomSimilarity(queryNorm=true): {}), locale=en-AU, timezone=Europe/Vienna
  2> NOTE: Linux 5.4.0-125-generic amd64/Oracle Corporation 18.0.2.1 (64-bit)/cpus=8,threads=1,free=465272544,total=536870912
  2> NOTE: All tests run in this JVM: [CoordinatorTests]

Tests with failures:
 - org.elasticsearch.cluster.coordination.CoordinatorTests.testSingleNodeDiscoveryStabilisesEvenWhenDisrupted
```


server/src/main/java/org/elasticsearch/cluster/coordination/Coordinator.java
optionalJoin.ifPresent(this::handleJoin);
                joinAccumulator.handleJoinRequest(joinRequest.getSourceNode(), joinListener);
                if (prevElectionWon == false && coordState.electionWon()) {
                    becomeLeader();
                }
            }
        } catch (Exception e) {
            joinListener.onFailure(e);
        }
    }
    private void updateSingleNodeClusterChecker() {
        assert Thread.holdsLock(mutex) : "Coordinator mutex not held";
        if (mode == Mode.LEADER && applierState.nodes().size() == 1) {
            if (singleNodeClusterChecker == null) {
                
                singleNodeClusterChecker = transportService.getThreadPool().scheduleWithFixedDelay(new Runnable() {
                    @Override
                    public void run() {
                        Coordinator.this.checkSingleNodeCluster();
                    }
                    @Override
                    public String toString() {
                        return "single-node cluster checker";
                    }
                }, this.singleNodeClusterSeedHostsCheckInterval, Names.SAME);
            }
            return;
        }
        
        if (singleNodeClusterChecker != null) {