Cesium 3D tileset causes UI shutdown in VR Core template

## Steps to reproduce

1. Start a new project, using Unity 2022.3.4 lts, and select VR Core as a template.
2. Install Cesium For Unity in project.
3. Open up BasicScene.unity.
4. Add Cesium World Terrain to the scene.
5. Hit play and the following error will appear:

```NullReferenceException: Object reference not set to an instance of an object
CesiumForUnity.CesiumCreditSystemUI.SetCreditsOnVisualElements (UnityEngine.UIElements.VisualElement onScreenElement, System.Collections.Generic.List`1[T] onScreenCredits, UnityEngine.UIElements.VisualElement popupElement, System.Collections.Generic.List`1[T] popupCredits, System.Boolean removeExtraSpace) (at ./Packages/com.cesium.unity/Runtime/CesiumCreditSystemUI.cs:347)
CesiumForUnity.CesiumCreditSystemUI.SetCredits (System.Collections.Generic.List`1[T] onScreenCredits, System.Collections.Generic.List`1[T] popupCredits) (at ./Packages/com.cesium.unity/Runtime/CesiumCreditSystemUI.cs:312)
CesiumForUnity.CesiumCreditSystem.BroadcastCreditsUpdate () (at ./Packages/com.cesium.unity/Runtime/CesiumCreditSystem.cs:184)
Reinterop.ReinteropInitializer.CesiumForUnity_CesiumCreditSystem_CallBroadcastCreditsUpdate_1B2M2Y8AsgTpgAmY7PhCfg (System.IntPtr thiz) (at ./Reinterop/Reinterop.RoslynSourceGenerator/ReinteropInitializer.cs:1961)
(wrapper native-to-managed) Reinterop.ReinteropInitializer.CesiumForUnity_CesiumCreditSystem_CallBroadcastCreditsUpdate_1B2M2Y8AsgTpgAmY7PhCfg(intptr)
CesiumForUnity.CesiumCreditSystem.UpdateCredits (System.Boolean forceUpdate) (at ./Reinterop/Reinterop.RoslynSourceGenerator/CesiumCreditSystem-generated.cs:60)
CesiumForUnity.CesiumCreditSystem.Update () (at ./Packages/com.cesium.unity/Runtime/CesiumCreditSystem.cs:161)
```