SyncedFoldersActivity: don't refresh entire adapter when toggling a folder from dialog

It's enough to refresh its header, and it doesn't have to refresh all pictures

Signed-off-by: Álvaro Brey <alvaro.brey@nextcloud.com>

app/src/main/java/com/owncloud/android/ui/activity/SyncedFoldersActivity.kt

@@ -672,8 +672,7 @@ class SyncedFoldersActivity :
             )
             saveOrUpdateSyncedFolder(item)
 
-            // TODO test if notifyItemChanged is sufficient (should improve performance)
-            adapter.notifyDataSetChanged()
+            adapter.notifyItemChanged(adapter.getSectionHeaderIndex(syncedFolder.section))
         }
         syncedFolderPreferencesDialogFragment = null
         if (syncedFolder.isEnabled) {