Problems generating BakedLightMaps by code

[maikramer]

Godot version:
ba134d4

OS/device including version:
Ubuntu 18.04

Issue description:
While trying to call the function BakedLightMap,Bake() i get in the console

ERROR: write_variant: Resource was not pre cached for the resource section, bug?
At: core/io/resource_format_binary.cpp:1508.

I debugged athe code and detected that the problem happens in

godot/core/io/resource_saver.cpp

Line 74 in ba134d4

err = saver[i]->save(p_path, p_resource, p_flags);

This happens while BakedLightMap tryes to save the ImageTexture in disk.

I guess that this issue is related to #18801, but as they are 2 totally diferent situations i decided to open a new issue.

Steps to reproduce:
Bake a lightmap by code.

[reduz]

This needs to be re-made in 3.2 with Vulkan, will kick there

[KoBeWi]

Seems fixed in 3.2.4 beta3 (no error on calling bake()).
Can't test in 4.0, because bake() method doesn't exist for some reason (even though you can see it in online docs)

If you can still reproduce, provide a minimal reproduction project.