Shader error in 'Toon/Toon': redefinition of '_Surface' when the package is installed

Reproduction steps:

1. Create a URP project
2. Open the Package Manager (Window > Package Management > Package Manager)
3. import the `com.unity.toonshader` package by clicking the “+” symbol and selecting “Import package by technical name”
4. Observe the Console

Actual result: A Shader error is shown: “'Toon/Toon': redefinition of '_Surface' at /Users/User/Documents/Unity/TT66/Library/PackageCache/com.unity.render-pipelines.universal@f5f4d476217d/Shaders/Utils/SurfaceType.hlsl(21)”
Expected result: No shader errors appear

Reproducible with: 0.10.1, 0.14.0 (6000.6.0a3)
Not reproducible with: 0.10.0 (6000.6.0a3)

Reproducible on: Windows 10 (by reporter), macOS 26.4.1 (M3 Max)
Not reproducible on: No other environments tested

Note: In version 0.10.0, a different error is still shown