Start work on rendering channel participants in collab panel

Co-authored-by: mikayla <mikayla@zed.dev>

crates/collab/src/tests.rs

@@ -103,6 +103,9 @@ impl TestServer {
 
     async fn create_client(&mut self, cx: &mut TestAppContext, name: &str) -> TestClient {
         cx.update(|cx| {
+            if cx.has_global::<SettingsStore>() {
+                panic!("Same cx used to create two test clients")
+            }
             cx.set_global(SettingsStore::test(cx));
         });