Add DB prefix to PHP tests (#1855)
Add DB prefix to PHP tests (#1855)

* Add test job with PHP 7.3, MySQL & custom prefix

* Add prefix MariaDB test

* Add PHP 7.4 to tests

* Remove PHP 7.4 from tests

This reverts commit 270cba2f5f3883cba856d891e3b2f5feda8a2b01.

flarum/core,flarum/core,flarum/core