[4.5] Can't convert `StandardMaterial3D` to `ShaderMaterial` in FileSystemDock

[beicause]

Tested versions

Reproducible in 4.5.beta1
Not reproduible in 4.4

System information

Linux

Issue description

Can't convert StandardMaterial3D to ShaderMaterial in FileSystemDock in 4.5.

However in inspector converting works well.

Steps to reproduce

Create a StandardMaterial3D, in FileSystemDock, convert it to ShaderMaterial

Minimal reproduction project (MRP)

N/A