Add a MariaDB 10.0 environment to help Pantheon users

Problem/Motivation

Although Drupal 9 requires MySQL 5.7 and MariaDB 10.3, some hosting platforms are still on older database versions. For example, there are Acquia customers on MySQL 5.6 and Pantheon customers on MariaDB 10.0. To support Drupal 9 on these older database versions, I maintain https://www.drupal.org/project/mysql56 → . I use 📌 Testing issue for mysql56 Needs work to periodically run Drupal 9 core's full test suite with this driver on MySQL 5.6 and MariaDB 10.2. However, MariaDB 10.0 and 10.1 are not available environments for me to request a test run for, so although https://www.drupal.org/project/mysql56 → claims to work on MariaDB 10.0, I can't verify if that's actually true.

Proposed resolution

Please add a MariaDB 10.0 environment. There's a separate issue for #2631466: MariaDB 10.1 → , and having both would be great, but if we can only have one, then 10.0 would be the more useful one, since that's the one that the Pantheon platform is currently using.