CameraAttributes exposure doesn't affect unshaded materials, but auto exposure does

### Tested versions

Reproducible in: 4.2.1,stable.official, 4.3.dev4.official

### System information

Godot v4.3.dev4 - Windows 10.0.22000 - Vulkan (Forward+) - integrated Intel(R) UHD Graphics (Intel Corporation; 26.20.100.7926) - Intel(R) Core(TM) i5-1035G1 CPU @ 1.00GHz (8 Threads)

### Issue description

Unshaded materials will correctly stay unshaded when manually adjusting a CameraAttributes' exposure, but enabling auto exposure will brighten/darken them. Additionally, the exposure shader parameter doesn't seem to be affected by auto exposure.
Happens in both Forward+ and Mobile renderers.

### Steps to reproduce

Make a mesh with an unshaded material. Make a WorldEnvironment, give it camera attributes, enable Auto Exposure. Put them in the same scene and watch the magic happen.

### Minimal reproduction project (MRP)

[Auto Exposure MRP.zip](https://github.com/godotengine/godot/files/14530919/Auto.Exposure.MRP.zip)

Start by running the linked Auto Exposure MRP.zip in Godot and reproduce the behavior with an unshaded material in both Forward+ and Mobile renderers. Compare manual CameraAttributes exposure with auto exposure, including the exposure shader parameter. Done means auto exposure no longer brightens or darkens unshaded materials unexpectedly and the shader parameter behaves consistently.

Written by the indexing model from the issue text.