Can't apply OpenY config in D9

Problem/Motivation

I can't apply OpenY config via the tool, it produces an error:

The website encountered an unexpected error. Please try again later.TypeError: call_user_func_array(): Argument #1 ($callback) must be a valid callback, class Drupal\config\Form\ConfigSync does not have a method "processBatch" in _batch_process() (line 295 of core/includes/batch.inc). _batch_do() (Line: 93)

\Drupal\config\Form\ConfigSync::processBatch() was deprecated in Drupal 8. See also https://git.drupalcode.org/project/drupal/-/commit/7ab5bbcee416e41212806....

Steps to reproduce

1. Go to /admin/openy/development/upgrade-log/dashboard with some changed config.
2. Click for the dirty config.
3. Click on the modal.

Proposed resolution

Either update to use \Drupal\Core\Config\Importer\ConfigImporterBatch (which isn't part of the public API IIUC so could feasibly change in a minor release) or copy over the functionality into this module.

Remaining tasks

User interface changes

API changes

Data model changes