Get server integration tests passing again

* Set up UserStore to have the current user, so that
  channel messages can be sent. This is needed now that
  pending messages are represented more similarly to
  regular messages.
* Drop buffer inside of an `AppContext.update` block, so that
  the Buffer's release hook is called in time.

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

zed/src/user.rs

@@ -111,8 +111,12 @@ impl UserStore {
             .ok_or_else(|| anyhow!("server responded with no users"))
     }
 
-    pub fn current_user(&self) -> &watch::Receiver<Option<Arc<User>>> {
-        &self.current_user
+    pub fn current_user(&self) -> Option<Arc<User>> {
+        self.current_user.borrow().clone()
+    }
+
+    pub fn watch_current_user(&self) -> watch::Receiver<Option<Arc<User>>> {
+        self.current_user.clone()
     }
 }