LightmapGI: Importing gltf with materials from Blender causes light bleeding at edges

### Tested versions

- `v4.5.dev4.official [209a446e3]` - main tested version
- `v4.4.1.stable.official [49a5bc7b6]` - looks worse even with no material export, might be a different unrelated issue

### System information

Godot v4.5.dev4 - EndeavourOS #1 ZEN SMP PREEMPT_DYNAMIC Fri, 09 May 2025 17:35:59 +0000 on Wayland - X11 display driver, Multi-window, 1 monitor - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1650 (nvidia; 570.144) - AMD Ryzen 5 5600H with Radeon Graphics (12 threads)

### Issue description

I get obvious light bleeding when I spawn a mesh with materials assigned in Blender and bake lightmaps with it:


This doesn't happen if I export the same model with materials disabled and set the same texture/roughness/metallic in Godot:


Might be related to #87815 but this happens even with a single manifold mesh and zero intersecting geometry. The baked EXR shows a bit of orange in places that should be pure black (saturation boosted, bad lightmap on top good on bottom):


### Steps to reproduce

- Download and run project
- Click on the screen or press space to switch camera

### Minimal reproduction project (MRP)

[light-bleeding.zip](https://github.com/user-attachments/files/20265516/light-bleeding.zip)

Start by running the linked light-bleeding.zip minimal reproduction project in the listed Godot versions, then compare the LightmapGI bake using Blender-exported materials with the bake using equivalent materials assigned in Godot. Inspect the LightmapGI and glTF material-import paths while reproducing the edge bleeding. Done means the imported-material case no longer produces the reported leaks without regressing the control case.

Written by the indexing model from the issue text.