[fenix] Close https://github.com/mozilla-mobile/fenix/issues/18934: Remove adapter when deataching from window

app/src/main/java/org/mozilla/fenix/tabstray/browser/BaseBrowserTrayList.kt

@@ -88,6 +88,9 @@ abstract class BaseBrowserTrayList @JvmOverloads constructor(
         tabsFeature.stop()
         swipeToDelete.stop()
 
+        // Release the adapter so that `onDetachedFromRecyclerView` will be called in the adapter.
+        adapter = null
+
         touchHelper.attachToRecyclerView(null)
     }
 }