Constant FILTER_SANITIZE_STRING is deprecated in ContactStorageExportService.php

FILTER_SANITIZE_STRING used to strip also tags, current solution does not, but that's ok, because we can safely assume that there will be no html from the field labels.
From my tests this works fine, but if we want the automated tests to also pass then we need:
https://www.drupal.org/project/contact_storage_export/issues/3219887 🐛 Fix test for drupal9 Fixed

one of these 2 will need to go first though, up to the maintainer.

Thank you Berdir, and thank you for testing and explaining as well to me Andras, much appreciated!

Automatically closed - issue fixed for 2 weeks with no activity.