For #6980: Show correct image mocks for toolbar positions

app/src/main/res/layout/onboarding_toolbar_position_picker.xml

@@ -68,7 +68,7 @@
         android:layout_height="wrap_content"
         android:layout_marginStart="16dp"
         android:layout_marginTop="16dp"
-        android:background="@drawable/onboarding_light_theme"
+        android:background="@drawable/onboarding_toolbar_top"
         android:contentDescription="@string/preference_top_toolbar"
         android:foreground="@drawable/rounded_ripple"
         app:layout_constraintEnd_toStartOf="@+id/toolbar_bottom_image"
@@ -97,7 +97,7 @@
         android:layout_marginStart="16dp"
         android:layout_marginTop="16dp"
         android:layout_marginEnd="16dp"
-        android:background="@drawable/onboarding_dark_theme"
+        android:background="@drawable/onboarding_toolbar_bottom"
         android:contentDescription="@string/preference_bottom_toolbar"
         android:foreground="@drawable/rounded_ripple"
         app:layout_constraintEnd_toEndOf="parent"