Add Qwen2-7B to the list of zed.dev models (#15649)

Release Notes:

- N/A

---------

Co-authored-by: Nathan <nathan@zed.dev>

crates/language_model/src/request.rs

@@ -37,6 +37,7 @@ impl LanguageModelRequest {
             stream: true,
             stop: self.stop,
             temperature: self.temperature,
+            max_tokens: None,
             tools: Vec::new(),
             tool_choice: None,
         }