Fix copying MIME type if scene nodes are copied

We're not doing this in the nicest way possible...

Contributes to issue CURA-8232.

cura/CuraApplication.py

@@ -1867,6 +1867,7 @@ class CuraApplication(QtApplication):
             else:
                 node = CuraSceneNode()
                 node.setMeshData(original_node.getMeshData())
+                node.source_mime_type = original_node.source_mime_type
 
                 # Setting meshdata does not apply scaling.
                 if original_node.getScale() != Vector(1.0, 1.0, 1.0):

cura/Scene/CuraSceneNode.py

@@ -142,6 +142,7 @@ class CuraSceneNode(SceneNode):
         copy.setTransformation(self.getLocalTransformation(copy= False))
         copy.setMeshData(self._mesh_data)
         copy.setVisible(cast(bool, deepcopy(self._visible, memo)))
+        copy.source_mime_type = cast(str, deepcopy(self.source_mime_type, memo))
         copy._selectable = cast(bool, deepcopy(self._selectable, memo))
         copy._name = cast(str, deepcopy(self._name, memo))
         for decorator in self._decorators: