Fix failing tests

Problem/Motivation

The tests are failing in the dev branch
Errors:

1) Drupal\Tests\fontyourface\Functional\FontYourFaceFontDisplayTest::testFontNotDisplayed
Error: Call to undefined method Drupal\Core\Extension\ThemeHandler::install()

/app/web/modules/contrib/fontyourface/tests/src/Functional/FontYourFaceFontDisplayTest.php:46
/app/vendor/phpunit/phpunit/src/Framework/TestResult.php:728

2) Drupal\Tests\fontyourface\Functional\FontYourFaceFontDisplayTest::testFontDisplayedViaFontDisplayRule
Error: Call to undefined method Drupal\Core\Extension\ThemeHandler::install()

/app/web/modules/contrib/fontyourface/tests/src/Functional/FontYourFaceFontDisplayTest.php:46
/app/vendor/phpunit/phpunit/src/Framework/TestResult.php:728

Steps to reproduce

Run tests

Proposed resolution

Change the \Drupal::service('theme_handler') in the setup to \Drupal::service('theme_installer')

Remaining tasks

User interface changes

API changes

Data model changes