Fog is weird in double precision

### Tested versions

- Reproducible https://github.com/V-Sekai/godot/commit/1d265a7208febe4c0dba90066e02a91cc532c1cd (doubles)
- Not reproducible: https://github.com/godotengine/godot/releases/tag/4.2.2-stable (single)

### Untested versions but suspicious

https://github.com/godotengine/godot/releases/tag/4.2.2-stable (double)

### System information

Windows 11, Nvidia 3090, Vulkan forward+

### Issue description

https://youtu.be/cNQ9ksd5cAw

Fog seems to be not working correctly. Seems to be split into layers instead of being even.

### Steps to reproduce

Turning on fog causes this to happen on https://github.com/V-Sekai/godot-crappy-contraptions/commit/0fff44fa1bf2e70c2ce295a4bbfdc27cd07dbf1b

### Minimal reproduction project (MRP)

[godot-crappy-contraptions-main.zip](https://github.com/godotengine/godot/files/15078404/godot-crappy-contraptions-main.zip)