DisconnectedAsync is not raised if (failed) Publish attempts were made

### Describe the bug

For my use case, I have a two-way application protocol, where I periodically send a message to a different MQTT client.
This seems to lead to `MqttClient.DisconnectedAsync` to never be invoked by the KeepAlive mechanism when the connection has been disrupted.

### Which component is your bug related to?
- Client

### To Reproduce
Steps to reproduce the behavior:
1. Using this version of MQTTnet v5.1.0.1559.
2. Connect an instance of MqttClient to a broker using a KeepAliveInteval of 5 seconds.
3. Start to publish messages once every second.
4. Stop the broker.
5. Wait for the `DisconnectedAsync` event to be raised.

### Expected behavior
The event is raised after at most 10s.

### Actual behavior
The event is never raised.

### Code example
```csharp
// Using Testcontainers.Mosquitto v4.10.0 to create a broker
await using var mosquitto = new MosquittoBuilder("eclipse-mosquitto:2.1.2-alpine")
.WithPortBinding(1883, assignRandomHostPort: true)
.Build();
await mosquitto.StartAsync();

using var client = new MqttClientFactory().CreateMqttClient();
await client.ConnectAsync(
new MqttClientOptionsBuilder()
.WithConnectionUri(mosquitto.GetConnectionString())
.WithKeepAlivePeriod(TimeSpan.FromSeconds(5))
.Build());

var disconnectedRaised = new TaskCompletionSource();
client.DisconnectedAsync += _ =>
{
disconnectedRaised.TrySetResult();
return Task.CompletedTask;
};

using var cts = new CancellationTokenSource(TimeSpan.FromSeconds(30));
var periodicPublishTask = Task.Run(async () =>
{
using var periodicTimer = new PeriodicTimer(TimeSpan.FromSeconds(1));
await using var cancelTimer = cts.Token.Register(periodicTimer.Dispose);

while (await periodicTimer.WaitForNextTickAsync(CancellationToken.None))
{
// When commenting this line, the keep alive mechanism does raise DisconnectedAsync event
await client.PublishStringAsync("any/topic", "Any message");
}
});

try
{
await mosquitto.PauseAsync(CancellationToken.None);

// This should definitely complete within the 30s, but times out
await disconnectedRaised.Task.WaitAsync(cts.Token);
}
finally
{
await cts.CancelAsync();
await periodicPublishTask;
}
```