Project Manager removes favourites on start up

### Tested versions

v4.3.dev5.official [89f70e98d]

### System information

Windows 11, Godot v4.3.dev5.official [89f70e98d]

### Issue description

The project manager removes the favourite markers on start up.

### Steps to reproduce

Mark project(s) as favourite in v4.2.1.stable.official [b09f793f5] for example.
Then open v4.3.dev5.official [89f70e98d] project manager and all favourites become unset.

Saving favourites works though. When I mark projects as favourite, and then open the project manager in 4.2.1 they are marked.

### Minimal reproduction project (MRP)

Just create an empty project and mark it as favourite.

Start by reproducing the favourite-marker loss in the Godot Project Manager when opening a project manager version after marking projects in another version. Compare the startup loading behavior with the reported case where saving favourites works, and consider the issue done when favourites persist across these versions on Windows 11.

Written by the indexing model from the issue text.