GridMap tiles have white dots on them while the camera is not moving.

### Tested versions

- Reproducible in v4.3.stable.mono.official [77dcf97d8]
- While it's a bit difficult to downgrade, I remember this existing from around v4.2.stable.mono.official [46dc27791] when I started adding graphics and using GridMap for the first time.

### System information

Godot v4.3.stable.mono - Windows 10.0.22631 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 3070 (NVIDIA; 31.0.15.3598) - AMD Ryzen 9 5950X 16-Core Processor (32 Threads)

### Issue description

(While I am primarily using a Windows machine, I have seen this happening on an OLED Steam Deck as well.)

I am using a GridMap in my game as a way to simplify level generation and have been doing a bit of stress testing in worst case conditions to see the performance of it, figure out how to approach it on optimization and whatnot. However, I've noticed from Godot 4.2 onwards is how something in my setup with the tiles is causing random white dot artifacts to appear on the tiles whenever I am not moving the camera around. I've tried to see if they might be present on other objects as well by adding them to the scene at random locations to look at, but the dots only seem to appear on the tiles themselves.

I've also tried creating a completely new project where I precreate a GridMap map with the same tiles that I've generated before, but haven't really noticed artifacts appearing in these situations, making it really difficult to understand what might be causing this.

One weird thing though is that when using regular sky lighting, these visual artifacts are still visible when ambient lighting is turned off for the tiles, meaning it's completely pitch black. Even weirder, while in sky lighting, turning on either fog setting in the world environment, even with 0 values and an invisible fog, makes these artifacts disappear completely, or at the very least making them really hard to notice. It's convenient for me since I wanted to use fog, but it shouldn't be something that's needed to avoid this kind of visual issue.

In the MRP project field, I've included a link that has 2 videos and a zip file of the project on this issue happening on my end.

Direct video links to Youtube:

[Video 1 with the main game application](https://youtu.be/AR-9T3Wcpvs)

[Video 2 with the MRP Project](https://youtu.be/NsYn_6NcQ0s)

### Steps to reproduce

The project that I am developing is a C# project and it's a bit too time consuming to create a completely pure GDScript version for recreation, so the MRP project should be opened with the Mono version of Godot, and then C# Building needs to be enabled through Project -> Tools -> C# -> Create C# Solution.

Once that's done and the project is started, the mouse is used as a simple first person camera, Escape closes the game, and the 1 and 2 keys can be used to change mouse control, so that the editor can be used while the game is open.

The game will then automatically generate a 300x300 grid filled with tiles.

If everything goes as expected, then there should be white dots visible when the camera is not moving around. You can also use the WorldEnvironment field during runtime to see how the dots react to different settings, such as disabling the ambient light and still seeing dots, or enabling fog with a sky background to make the dots disappear.

### Minimal reproduction project (MRP)

Link to files: https://drive.proton.me/urls/AV8N8QQ7YG#vD6phrEfIQBB

Open the linked MRP with the Mono version of Godot, enable C# building, and reproduce the 300x300 GridMap under Vulkan Forward+. Start by varying camera movement, ambient lighting, sky lighting, and WorldEnvironment fog as described; done means isolating the conditions that produce or hide the white dots and documenting a reproducible cause or fix.

Written by the indexing model from the issue text.