[SideSheet] Fixed container color assigned to incorrect attribute.

Should be `app:backgroundTint` not `android:background`.

PiperOrigin-RevId: 523147016

lib/java/com/google/android/material/sidesheet/res/values/styles.xml

@@ -19,7 +19,7 @@
   <!-- Style for the M3 Standard Side Sheet. -->
   <style name="Widget.Material3.SideSheet" parent="">
     <item name="enforceMaterialTheme">true</item>
-    <item name="android:background">@macro/m3_comp_sheet_side_docked_container_color</item>
+    <item name="backgroundTint">@macro/m3_comp_sheet_side_docked_container_color</item>
     <!-- Layout_* attributes break when set via a default style, but it's ok to
          set layout_* attributes from this style, because this style always
          needs to be explicitly set on the behavior's associated View in the