Use the right max_token_count for Qwen

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

crates/language_model/src/model/cloud_model.rs

@@ -32,7 +32,7 @@ impl ZedModel {
 
     pub fn max_token_count(&self) -> usize {
         match self {
-            ZedModel::Qwen2_7bInstruct => 8192,
+            ZedModel::Qwen2_7bInstruct => 28000,
         }
     }
 }