moving to a newer runner image means using MySQL 8, which needs a workaround for PHP <=7.3
the workaround wasn't working for PHP 7.0 or 5.6, so these have been removed.
PHP 8.1 and 8.2 can't be added until PHPUnit version is increased.
The new block editor sidebar wasn't appearing before WP 5.7, so don't test before that, with a view to bumping minimum WP (and PHP) version numbers in a future release.
Description
Deploy Notes
None.
Steps to Test
See the passed workflows.