Fix CSPELL-PHPCS issues for branch 8.x-1.x

All jobs are green now, so I'll merge it to the 8.x-1.x branch now: https://git.drupalcode.org/project/many_selects/-/merge_requests/10

Merged to 8.x-1.x now, I'll mark this as "Fixed", I won't include tests here because the Drupal Core version is not compatible with the Gitlab CI/CD configuration.