Cannot stop the server

Nobody has claimed this yet.

Hey, as in issue title. I wanted to test that a service gracefully handles networking issues like server being temporarily unreachable and wanted to do that by dropping the `MockServer`, however this loop actually never finishes:
```rs
use std::time::Duration;

use tokio::{net::TcpStream, time::sleep};
use wiremock::MockServer;

#[tokio::main]
async fn main() {
let server = MockServer::start().await;
let addr = *server.address();

drop(server);

loop {
if TcpStream::connect(addr).await.is_err() {
break;
}
sleep(Duration::from_millis(200)).await;
println!("retrying");
}
}
```

Start with MockServer::start().await and MockServer::address() in the reproduction; verify what dropping MockServer is expected to do and why TcpStream::connect(addr) remains successful. Reproduce the loop, then check that the lifecycle behavior is corrected so dropping the server makes the connection fail and the loop exits.

Written by the indexing model from the issue text.