Scriptable Audio Processor RootOutput isn't Bursted at runtime

Steps to reproduce:

1. Create a `RootOutputInstance.IRealTime` and add `[BurstCompile]` to it
2. Observe that Burst compiles the processor correctly in the Burst Inspector

Actual results: The processor runs in the normal managed C# VM

Expected results: The processor runs in Burst

Reproducible with versions: 

Not reproducible with versions: 

Can’t test with versions: 

Tested on (OS): 

Notes:

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