[Dual Shade] Fix ShadeHeaderViewModelTest for Dual Shade on by default.

This ensures these unit tests do not fail when Dual Shade is the default
shade experience in scene container.

Bug: 376411622
Test: Updated unit tests.
Flag: com.android.systemui.scene_container
Change-Id: Iccac8202afe54062b892c6efb0ce777d7a4054f9