Give a better error message when the user tries to register a node having the same id as an internal one. Before: `RuntimeError: Error: Registering node class: 'NodeDummy', bl_idname 'NodeGroupInput' could not be unregistered` After: `RuntimeError: Error: Registering node class: 'NodeDummy', bl_idname 'NodeGroupInput' is an internal node` This is a followup to #111615 Authored-By: @vitorboschi (Vitor Boschi) Pull Request: https://projects.blender.org/blender/blender/pulls/111799