Gradient Mapped With GPU Expression

Steps to reproduce:

1. Import attached VFX in a scene, either HDRP or URP project
2. Observe console error

Actual results: 
Compilation error
```Shader error in 'Hidden/VFX/Repro_Gradient/Simple Loop/Render Quad': undeclared identifier 'attributes' at /(2475) (on d3d11)```

Expected results: 
No compilation error, there are some known limitation regarding slot being evaluated on CPU (like submesh mask) but this one is a GPU evaluation.

Reproducible with versions: 6000.4.0a3 (and other to define) 

Not reproducible with versions: N/A

Can’t test with versions: N/A

Tested on (OS): Windows

Notes:

• See https://discussions.unity.com/t/vfx-graph-bug-unity-6-3-output-particle-unlit-quad-undeclared-identifier-attributes/1689214
• This following case compiles and should have the same constraint: