Add logic for closed beta LLM models (#16482)

Release Notes:

- N/A

---------

Co-authored-by: Marshall <marshall@zed.dev>

crates/collab/src/tests/test_server.rs

@@ -667,6 +667,7 @@ impl TestServer {
                 google_ai_api_key: None,
                 anthropic_api_key: None,
                 anthropic_staff_api_key: None,
+                llm_closed_beta_model_name: None,
                 clickhouse_url: None,
                 clickhouse_user: None,
                 clickhouse_password: None,