[bc25] Fix notifications showing above QS shade (in Dual Shade mode).

Notifications can still show above QS shade when the HUN appears, but
this will be fixed separately (b/372000794).

Fix: 371554945
Bug: 372000794
Flag: com.android.systemui.scene_container
Flag: com.android.systemui.dual_shade
Test: Manually tested by expanding and collapsing the quick settings
shade over both lockscreen and gone, as well as invoking the HUN on QS.
Test: Existing unit tests still pass.

Change-Id: I0e84aaf628131c4534081b787ca1286ea1c069f1