With reactor-core >3.3.5, Calling WebSocketSession.close() in client.execute(uri, handler) logs an error

Hi,

The following test code connects to a websocket server and then closes the connection (to prove that the server is correctly accepting websockets connections):
```java
@Test
public void echo() {
WebSocketClient client = new StandardWebSocketClient();
client.execute(getUrl("/notify"), WebSocketSession::close).block();
}
protected URI getUrl(String path) {
return URI.create("ws://localhost:" + this.port + path);
}
```

With reactor 3.3.4, it works as expected. With reactor 3.3.5, even though the test still works, I get the following log:
```
17:05:26.766 [Grizzly(1)] ERROR reactor.core.publisher.Operators - Operator called default onErrorDropped
java.lang.IllegalStateException: The connection has been closed.
at org.glassfish.tyrus.core.TyrusSession.checkConnectionState(TyrusSession.java:513)
Suppressed: reactor.core.publisher.FluxOnAssembly$OnAssemblyException:
Error has been observed at the following site(s):
|_ checkpoint ⇢ ws://localhost:46257/notify [StandardWebSocketHandlerAdapter]
Stack trace:
at org.glassfish.tyrus.core.TyrusSession.checkConnectionState(TyrusSession.java:513)
at org.glassfish.tyrus.core.TyrusSession.close(TyrusSession.java:208)
at org.springframework.web.reactive.socket.adapter.StandardWebSocketSession.close(StandardWebSocketSession.java:103)
at org.springframework.web.reactive.socket.WebSocketSession.close(WebSocketSession.java:89)
at org.springframework.web.reactive.socket.adapter.AbstractListenerWebSocketSession.onComplete(AbstractListenerWebSocketSession.java:218)
at reactor.core.publisher.StrictSubscriber.onComplete(StrictSubscriber.java:123)
at reactor.core.publisher.Operators.complete(Operators.java:135)
at reactor.core.publisher.MonoEmpty.subscribe(MonoEmpty.java:45)
at reactor.core.publisher.Mono.subscribe(Mono.java:4218)
at org.springframework.web.reactive.socket.adapter.StandardWebSocketHandlerAdapter.onOpen(StandardWebSocketHandlerAdapter.java:86)
at org.glassfish.tyrus.core.TyrusEndpointWrapper.onConnect(TyrusEndpointWrapper.java:750)
at org.glassfish.tyrus.core.TyrusWebSocket.onConnect(TyrusWebSocket.java:139)
at org.glassfish.tyrus.client.TyrusClientEngine.processUpgradeResponse(TyrusClientEngine.java:554)
at org.glassfish.tyrus.client.TyrusClientEngine.handleSwitchProtocol(TyrusClientEngine.java:317)
at org.glassfish.tyrus.client.TyrusClientEngine.processResponse(TyrusClientEngine.java:254)
at org.glassfish.tyrus.container.grizzly.client.GrizzlyClientFilter.handleHandshake(GrizzlyClientFilter.java:322)
at org.glassfish.tyrus.container.grizzly.client.GrizzlyClientFilter.handleRead(GrizzlyClientFilter.java:291)
at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:283)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:200)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:132)
at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:111)
at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:536)
at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56)
at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:591)
at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:571)
at java.base/java.lang.Thread.run(Thread.java:834)
```

I tried defering the call to close() hoping it was some kind of race condition by using the following instead:
```java
client.execute(getUrl("/notify"), webSocketSession ->
Mono.empty().delaySubscription(Duration.ofMillis(5000))
.then(Mono.defer(webSocketSession::close))
).block()
```
But I still get the spurious error log.

I'm using org.glassfish.tyrus.bundles:tyrus-standalone-client 1.17

Is the spurious log a bug in my code or in the library ?
Thanks,
Jon