Fix datetime not serializable

src/scripts/update_all_request_files.py

@@ -18,13 +18,13 @@ def update_models(file_path, models):
                 data['still_on_hub'] = False
                 data['likes'] = 0
                 data['downloads'] = 0
-                data['created_at'] = None
+                data['created_at'] = ""
                 continue
 
             model_cfg = models[model_id]
             data['likes'] = model_cfg.likes
             data['downloads'] = model_cfg.downloads
-            data['created_at'] = model_cfg.created_at
+            data['created_at'] = str(model_cfg.created_at)
             #data['params'] = get_model_size(model_cfg, data['precision'])
             data['license'] = model_cfg.card_data.license if model_cfg.card_data is not None else ""