Lightmap UV discrepancies between Windows and Mac M1, despite identical source model, settings and unwrap_cache

### Tested versions

Reproduced in:
- 4.6.1.stable for Windows and Mac
- 4.6.1.stable.mono for Windows and Mac
- 4.5.1.stable for Windows and Mac
- 4.5.1.stable.mono for Windows and Mac

### System information

OpenGL API 4.1 Metal - 90.5 - Compatibility - Using Device: Apple - Apple M1 Max. Also Windows 11 on x86_64 real-life machine and Windows 11 on Parallels ARM Virtual Machine

### Issue description

For a small subset of our 3D models, we see discrepancies in the baked light maps between Windows and Mac M1.
All sources are identical: Model file, import settings, unwrap_cache.
If we bake lights on a Mac M1, we get "garbled" light maps on Windows.
Likewise, if we bake on Windows, it looks "garbled" on Mac M1, in a similar way.

Reference photos:
A: Baked on Mac M1 - viewed on Mac M1 (Correct)

B: Baked on Mac M1 - viewed on Windows (Garbled)

C: Baked on Windows - viewed on Windows (Correct)

D: Baked on Windows - viewed on Mac M1 (Garbled, but not identical to B)

### Steps to reproduce

*From scratch*
Import the Transfervessel model from the reproduction project.
Import it and produce a light bake.
Open the project on another platform (Mac <-> Windows), notice the light maps look incorrect.

*Or if using the reproduciton project*
Open the reproduciton project on a Mac, notice the light maps look correct.
Open the reproduction project on Windows, notice the light maps look incorrect.

### Minimal reproduction project (MRP)

Simple light baked scene, baked on Mac M1 (Reduced resolution to fit within upload size limit)

[lightmap-uv-inconsistencies-mrp-baked-on-mac-m1.zip](https://github.com/user-attachments/files/26182535/lightmap-uv-inconsistencies-mrp-baked-on-mac-m1.zip)

Start by opening the attached minimal reproduction project and reproducing the light bake on Windows and Mac M1 using the listed Godot versions. Compare the generated lightmap results and platform-specific behavior; done means the same source model, settings, and unwrap_cache produce matching lightmaps across both platforms.

Written by the indexing model from the issue text.