GPUParticles2D trails disappeared later than the particles

### Tested versions

- Reproducible in: 4.5.1-stable

### System information

Godot v4.5.1.stable - Windows 11 (build 26200) - Multi-window, 1 monitor - Vulkan (Forward+) - dedicated AMD Radeon RX 6750 GRE 12GB (Advanced Micro Devices, Inc.; 32.0.21037.1004) - AMD Ryzen 5 7500F 6-Core Processor (12 threads) - 31.71 GiB memory

### Issue description

The trails disappeared later than the particles. I think the trails disappeared at the same time as the particles or even earlier than the particles.

### Steps to reproduce

1. Create a GPUParticle2D node
2. Set the Amount to 300
3. Set the Lifetime to 8s
4. Check the "Trails" option and set the Lifetime of Trails to 0.6s
5. Add a "particleProcessMateria"l to the "ProcessMaterial" options
6. Slightly adjust the velocity in the "Spawn" section and Color and Curve in the "display" section

### Minimal reproduction project (MRP)

[the-trails-disappeared-later-than-the-particles.zip](https://github.com/user-attachments/files/24658495/the-trails-disappeared-later-than-the-particles.zip)

Open the attached minimal reproduction project and follow the listed GPUParticles2D setup in Godot 4.5.1. Observe the particle and trail lifetimes, then trace the GPUParticles2D trail behavior in the engine; done means trails disappear at the intended time relative to their particles.

Written by the indexing model from the issue text.