**Build scan:**
https://gradle-enterprise.elastic.co/s/w5uoitwbjlubk/tests/:server:test/org.elasticsearch.transport.RemoteClusterConnectionTests/testCloseWhileConcurrentlyConnecting

**Reproduction line:**
```
./gradlew ':server:test' --tests "org.elasticsearch.transport.RemoteClusterConnectionTests.testCloseWhileConcurrentlyConnecting" -Dtests.seed=1D1BC140B0F8A67C -Dtests.locale=sk -Dtests.timezone=Africa/Blantyre -Druntime.java=20
```

**Applicable branches:**
main

**Reproduces locally?:**
No

**Failure history:**
https://gradle-enterprise.elastic.co/scans/tests?tests.container=org.elasticsearch.transport.RemoteClusterConnectionTests&tests.test=testCloseWhileConcurrentlyConnecting

**Failure excerpt:**
```
com.carrotsearch.randomizedtesting.UncaughtExceptionError: Captured an uncaught exception in thread: Thread[id=1746, name=Thread-113, state=RUNNABLE, group=TGRP-RemoteClusterConnectionTests]


  Caused by: java.lang.AssertionError: cluster:internal/remote_cluster/handshake

    at __randomizedtesting.SeedInfo.seed([1D1BC140B0F8A67C]:0)
    at org.elasticsearch.transport.InboundAggregator.lambda$new$0(InboundAggregator.java:46)
    at org.elasticsearch.transport.InboundAggregator.initializeRequestState(InboundAggregator.java:197)
    at org.elasticsearch.transport.InboundAggregator.headerReceived(InboundAggregator.java:66)
    at org.elasticsearch.transport.InboundPipeline.forwardFragments(InboundPipeline.java:138)
    at org.elasticsearch.transport.InboundPipeline.doHandleBytes(InboundPipeline.java:121)
    at org.elasticsearch.transport.InboundPipeline.handleBytes(InboundPipeline.java:86)
    at org.elasticsearch.transport.netty4.Netty4MessageInboundHandler.channelRead(Netty4MessageInboundHandler.java:63)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
    at io.netty.handler.logging.LoggingHandler.channelRead(LoggingHandler.java:280)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:442)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
    at io.netty.handler.codec.MessageToMessageDecoder.channelRead(MessageToMessageDecoder.java:103)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:444)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
    at io.netty.channel.AbstractChannelHandlerContext.fireChannelRead(AbstractChannelHandlerContext.java:412)
    at io.netty.channel.DefaultChannelPipeline$HeadContext.channelRead(DefaultChannelPipeline.java:1410)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:440)
    at io.netty.channel.AbstractChannelHandlerContext.invokeChannelRead(AbstractChannelHandlerContext.java:420)
    at io.netty.channel.DefaultChannelPipeline.fireChannelRead(DefaultChannelPipeline.java:919)
    at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:166)
    at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:788)
    at io.netty.channel.nio.NioEventLoop.processSelectedKeysPlain(NioEventLoop.java:689)
    at io.netty.channel.nio.NioEventLoop.processSelectedKeys(NioEventLoop.java:652)
    at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:562)
    at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:997)
    at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
    at java.lang.Thread.run(Thread.java:1623)

```
server/src/test/java/org/elasticsearch/transport/RemoteClusterConnectionTests.java
barrier.await();
                                for (int j = 0; j < numGetCalls; j++) {
                                    try {
                                        Transport.Connection lowLevelConnection = connection.getConnection();
                                        assertNotNull(lowLevelConnection);
                                    } catch (NoSuchRemoteClusterException e) {
                                        
                                    }
                                }
                            } catch (Exception ex) {
                                throw new AssertionError(ex);
                            }
                        });
                        getThreads[i].start();
                    }
                    for (int i = 0; i < modifyingThreads.length; i++) {
                        final int numDisconnects = randomIntBetween(5, 10);
                        modifyingThreads[i] = new Thread(() -> {
                            try {
                                barrier.await();
                                for (int j = 0; j < numDisconnects; j++) {
                                    DiscoveryNode node = randomFrom(discoverableNodes);
                                    try {
                                        connection.getConnectionManager().getConnection(node);
                                    } catch (NoSuchRemoteClusterException e) {
                                        
                                    }
                                }
                            } catch (Exception ex) {
                                throw new AssertionError(ex);