SoftBody3D loses attachment offsets upon being loaded in the Editor

### Tested versions

- Reproducible in 4.6.stable

### System information

Godot v4.6.stable - Windows 10 (build 19045) - Multi-window, 2 monitors - Vulkan (Forward+) - dedicated NVIDIA GeForce GTX 1060 6GB (NVIDIA; 32.0.15.8180) - AMD Ryzen 5 3600 6-Core Processor (12 threads) - 15.93 GiB memory

### Issue description

Upon loading a scene containing SoftBody3D any modifications made to attachments//offset properties are lost, as if the Spatial Attachment had been freshly assigned.

### Steps to reproduce

1. Create a scene containing a SoftBody3D node. Pin at least one vertices and modify its Offset.
2. Save the scene.
3. Load the scene.

### Minimal reproduction project (MRP)

N/A