Fix step file

python/jupytercad_core/jupytercad_core/step_ydoc.py

@@ -28,8 +28,7 @@ def set(self, value: str) -> None:
         :param value: The content of the document.
         :type value: Any
         """
-        with self._ydoc.transaction() as t:
-            self._ysource.extend(t, value)
+        self._ysource[:] = value
 
     def observe(self, callback: Callable[[str, Any], None]):
         self.unobserve()