[fenix] For https://github.com/mozilla-mobile/fenix/issues/27734: Make tab tray overflow menu background layer2

This matches with the toolbar overflow menu.

app/src/main/java/org/mozilla/fenix/tabstray/ext/BrowserMenu.kt

@@ -18,7 +18,7 @@ fun BrowserMenu.showWithTheme(view: View) {
         (popupMenu.contentView as? CardView)?.setCardBackgroundColor(
             ContextCompat.getColor(
                 view.context,
-                R.color.fx_mobile_layer_color_1,
+                R.color.fx_mobile_layer_color_2,
             ),
         )
     }