default_bus_layout.tres is generated at old location after moved

[timothyqiu]

Godot version: 3.2.3 / 3.3 RC9 / master (c7a4e21)

OS/device including version: macOS 11.2.3 (not graphics-related)

Issue description:

After dragging default_bus_layout.tres into a subfolder, changing the bus layout still generates the layout file at old location.

Restarting the editor solves this issue.

Steps to reproduce:

1. Add a bus in the Audio tab so that res://default_bus_layout.tres appears in FileSystem.
2. Create a new folder resources, and drag default_bus_layout.tres into the folder.
   • The audio/buses/default_bus_layout in Project Settings is changed to res://resources/default_bus_layout.tres
3. Add another bus in the Audio tab
   • res://default_bus_layout.tres is generated again

Minimal reproduction project: Any empty project will do.