Return batch size from mutation response

Author: ramy1951

labelbox/schema/project.py

@@ -794,7 +794,7 @@ def _create_batch_sync(self, name, dr_ids, global_keys, priority,
                                   timeout=180.0,
                                   experimental=True)["project"][method]
         batch = res['batch']
-        batch['size'] = len(dr_ids)
+        batch['size'] = res['batch']['size']
         return Entity.Batch(self.client,
                             self.uid,
                             batch,