GPUParticles3D.color_ramp doesn't work

As of Godot 4.3.stable, color_ramp will not have an effect unless the materials in the draw pass are configured correctly: ¹

• For BaseMaterial3D, BaseMaterial3D.vertex_color_use_as_albedo must be true.
• For ShaderMaterial, ALBEDO *= COLOR.rgb; must be inserted in the shader's fragment() function.