Ambient light not affecting gridmap in compatibility renderer

[Wiggan]

Godot version

4.0.1rc1

System information

Windows10, AMD Ryzen 9 5900X, NVIDIA GeForce RTX 3060 Ti, driver version 30.0.15.1179, compatibility.

Issue description

Ambient lighting set in the environment does not affect gridmaps when using the compatibility render pipeline.

Steps to reproduce

Just add a gridmap and turn up ambient light. See how everything else gets bright but not the gridmap.

Minimal reproduction project

godot_repex.zip

[clayjohn]

This looks like it may be a duplicate of #74111