Instanced, locked scenes become unlocked on scene reload

[djrain]

Godot version:
3.3 RC8

OS/device including version:
macOS Big Sur
M1 Mac Mini

Issue description:
Instanced scenes that are locked in editor become unlocked upon reopening the scene. This is very frustrating when working with large scenes with lots of instances.

Steps to reproduce:

• instance a scene in another scene
• lock the instance
• save, close and reopen the scene

[akien-mga]

I can confirm the issue. I thought it was a regression but apparently not, the same happens in 3.2.3 and 3.2.

[akien-mga]

Related to #8322.

[KoBeWi]

Duplicate of #12838