Test against MySQL 8.4 (the new LTS) in general matrix

[GuySartorelli]

MySQL have released MySQL 8.4 which is a new LTS release

We recently made the decision to support LTS versions of MySQL so we should update the matrix to test against this version, and make any code changes that are necessary for CI to be green.

We'll keep testing MySQL 8.0 alongside 8.4 LTS.

Acceptance criteria

• CMS 5 MySQL 8.0, 8.4, 5.7 in CI + mariadb - php 8.1, 8.2, 8.3
• CMS 6 MySQL 8.0, 8.4 in CI + mariadb - php 8.3 for all, though would introduce new php versions as they're released
• CMS 4 branches test whatever they currently test (i.e. no change for CMS 4 CI runs)
• recipe kitchen sink ci should test only against mysql 8.4
• CI is green for all supported modules.

Test runs

• CMS 5 https://github.com/emteknetnz/silverstripe-campaign-admin/actions/runs/11883621325
• CMS 6 https://github.com/emteknetnz/silverstripe-campaign-admin/actions/runs/11883622245
• .env file is echoed in Final Preparation step so we can validate the port 3384 is used for MySQL 8.4 jobs

PRs

• ENH Add MySQL 8.4 gha-ci#159
• ENH Add MySQL 8.4 to matrix #112

[GuySartorelli]

PRs merged. Reassigned to steve to check it is correct for all supported CMS versions

[emteknetnz]

Things are working as expected
CMS 5 - https://github.com/silverstripe/silverstripe-campaign-admin/actions/runs/11904968239
CMS 6 - https://github.com/silverstripe/silverstripe-campaign-admin/actions/runs/11904969508