ssh remoting: Fix SSH connection not being closed (#18329)

This fixes the `SshSession` being leaked.

There were two leaks:

1. `Arc<SshSession>` itself got leaked into the `SettingsObserver` that
   lives as long as the application. Fixed with a weak reference.
2. The two tasks spawned by an `SshSession` had a circular dependency
   and didn't exit while the other one was running. Fixed by fixing (1)
   and then attaching one of the tasks to the `SshSession`, which means
   it gets dropped with the session itself, which leads the other task
   to error and exit.

Co-authored-by: Bennet <bennet@zed.dev>

Release Notes:

- N/A

---------

Co-authored-by: Bennet <bennet@zed.dev>

crates/project/src/project_settings.rs

@@ -334,17 +334,20 @@ impl SettingsObserver {
             .log_err();
         }
 
+        let weak_client = ssh.downgrade();
         cx.observe_global::<SettingsStore>(move |_, cx| {
             let new_settings = cx.global::<SettingsStore>().raw_user_settings();
             if &settings != new_settings {
                 settings = new_settings.clone()
             }
             if let Some(content) = serde_json::to_string(&settings).log_err() {
-                ssh.send(proto::UpdateUserSettings {
-                    project_id: 0,
-                    content,
-                })
-                .log_err();
+                if let Some(ssh) = weak_client.upgrade() {
+                    ssh.send(proto::UpdateUserSettings {
+                        project_id: 0,
+                        content,
+                    })
+                    .log_err();
+                }
             }
         })
         .detach();