Environment / Ambient Lighting from Skybox is Missing

Environment / Ambient Lighting from the Skybox is missing.
Surfaces lit exclusively by the skybox will appear black.

**How to reproduce**

See https://github.com/jfoshee/Hello-Cube/actions for a repro case

- Create a new Unity project using 3D template
- Select the default SampleScene for the build
- Add a default Cube to the Scene
- Add a behavior to rotate the camera to be able to see all sides of the cube
- Build the project using GameCI and observe that 3 sides of the cube are black (unlit)

**Expected behavior**

You should see all sides of the cube are illuminated. 3 sides will be brighter because they face the default directional light. The three opposite sides will be dimly lit because they are only lit by environment/ambient light.

**Additional details**

The relevant settings are found in the Unity editor under:

- Window > Rendering > Lighting
- Environment tab
- Under Environment Lighting header, select Source drop-down

I tested to see if this occurs with a non-default skybox, and verified it does still occur in that case.

**Work-Around**

Using a solid-color ambient lighting seems to work fine. That is, change the Environment Lighting Source to Color and select an appropriate color.