agent_ui: Fix signed-in check in Zed provider configuration (#36639)

This PR fixes the check for if the user is signed in in the Agent panel
configuration.

Supersedes https://github.com/zed-industries/zed/pull/36634.

Release Notes:

- Fixed the user's plan badge near the Zed provider in the Agent panel
not showing despite being signed in.

crates/agent_ui/src/agent_configuration.rs

@@ -192,7 +192,7 @@ impl AgentConfiguration {
         let is_signed_in = self
             .workspace
             .read_with(cx, |workspace, _| {
-                workspace.client().status().borrow().is_connected()
+                !workspace.client().status().borrow().is_signed_out()
             })
             .unwrap_or(false);