assistant: Dismiss model selector after changing model (#15974)

Co-Authored-By: Thorsten <thorsten@zed.dev>

Release Notes:

- N/A

Co-authored-by: Thorsten <thorsten@zed.dev>

crates/assistant/src/model_selector.rs

@@ -1,4 +1,5 @@
 use feature_flags::ZedPro;
+use gpui::DismissEvent;
 use language_model::{LanguageModel, LanguageModelAvailability, LanguageModelRegistry};
 use proto::Plan;
 
@@ -132,6 +133,8 @@ impl PickerDelegate for ModelPickerDelegate {
                 model.is_selected = model.model.id() == selected_model_id
                     && model.model.provider_id() == selected_provider_id;
             }
+
+            cx.emit(DismissEvent);
         }
     }