Beta 10 version is incompatible with PHP 7.4

Problem

Beta 8 version is incompatible with PHP 7.4

Steps to reproduce

1. Make sure that your system has PHP 7.3 or 7.4 (Drupal 9 minimal requirements)
2. Run "drush cr"
3. Observe the error "PHP Parse error: syntax error, unexpected '|', expecting ';' or '{' in /var/www/public/docroot/modules/contrib/uswds_ckeditor_integration/src/Form/GridDialog.php on line 56"

Line 56 of GridDialog.php has code that generates fatal error in any version of PHP lower than 8.0: the union type specified by pipe character |. The module page says that it is compatible with PHP version starting with 7.2. Drupal 9 minimal requirement is 7.3

Proposed resolution

Change the code, make it compatible with PHP ver. 7.3 as D9 minimal version.