How to reproduce:
1. Create a new project
2. Create Assets > Create > Visual Scripting > Script Graph and in the Inspector click Edit Graph
3. Go to File > Build Settings… and click on WebGL > Switch Platform > Build

Expected result: Build is successful
Actual result: Build was canceled and errors appear in the console

Reproducible with: 2021.2.0a19, 2021.2.0b16, 2022.0a13
Not reproducible with: 2020.3.20f1, 2021.1.24f1, 2021.2.0a17
Could not test: 2019.4.31f1 (Scripting Machine not working), 2021.2.0a18 (constantly failing to install this version and WebGL support)

Notes:
- Successfully builds to standalone Player
- No errors entering Play Mode

Errors:
Assets/Unity.VisualScripting.Generated/VisualScripting.Core/AotStubs.cs(850,64): error CS0306: The type 'ReadOnlySpan<char>' may not be used as a type argument
Or
Assets/Unity.VisualScripting.Generated/VisualScripting.Core/AotStubs.cs(842,11): error CS0234: The type or namespace name 'ReadOnlySpan<>' does not exist in the namespace 'System' (are you missing an assembly reference?)