Shader materials are not imported by the headless build

[Dragoncraft89]

Godot version:
3.2.1 headless build

OS/device including version:
Debian 10. Probably every Linux/BSD

Issue description:
Attempted to export the project in the CI/CD. We don't have the .import directory pushed to VC, as this is optional according to the docs.

Therefore before the game can be exported, some files need to be imported. This works fine for most files, but shader materials in escn files are ignored.

For comparison, I've included both files in a zip: (Opening in a normal text editor is enough to see that the headless import lacks the shader)
models.zip

It seems like shader materials are just stripped from the imported file in the headless build, as the same model works with a spatial material.

Steps to reproduce:
Extract the attached sample project. Export the project with godot --export "Test" test and run it with "./test". The material should be correctly loaded.

Now, rm -r .import/ to force a reimport. Export the project with godot_headless --export "Test" test_headless and run it. The material should be missing.

Minimal reproduction project:
headless_shader_import.zip

Edit: fixed project zip

[afk-mario]

This happened to me, it's weird because it worked on 3.4 and stopped working on 3.5

[Calinou]

Duplicate of #55711.