APV Sky occlusion doesn't consider the terrain

Steps to reproduce:

1. Open attached repro project
2. Load the "SampleScene" scene
3. Rebake probes (Generate Lighting)
4. Observe the game view and make sure probe sky occlusion is enabled in Probe Volumes section

Actual results: 

Room is heavily over exposed

Expected results: 

Room is dark with all light coming through the intrance. 

Reproducible with versions: 6000.2

Not reproducible with versions: 2023.3.a18

Can't test with versions: 2023.3.a17 (feature not available yet)

Tested on (OS): Windows

Notes:

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