Tests: Rename classes in phpunit/tests/formatting/
per the naming conventions.
https://make.wordpress.org/core/handbook/testing/automated-testing/writing-phpunit-tests/#naming-and-organization
Follow-up to [47780], [48911], [49327], [50291], [50292], [50342], [50452], [50453], [50456], [50967], [50968], [50969], [51491], [51492], [51493].
See #53363.