Repair wp/5.6 branch Actions: Pin MariaDB to 10.5 in CI - #622

What?

Pins the MariaDB version wp-env uses in this branch's CI to 10.5, by setting WP_ENV_MARIADB_VERSION: '10.5' in the workflow-level env: of end2end-test.yml and unit-test.yml.

Why?

Without a pin, wp-env runs the floating mariadb:latest image: whatever the newest MariaDB release is at the time, many years newer than anything WordPress 5.6 was released against. 10.5 is the latest MariaDB LTS release that came out before WordPress 5.6, so the database now matches that release's era.

How?

Uses the WP_ENV_MARIADB_VERSION environment variable added in #575. On this branch that is the only mechanism: wp-env has no mariadbVersion option here, and the generated Docker Compose file uses image: 'mariadb:${WP_ENV_MARIADB_VERSION:-latest}' for its single, shared mysql service. wp-env runs docker compose without overriding the environment, so the variable reaches Compose's variable substitution straight from the job environment. A workflow-level env: covers every job, including all four End-to-End jobs and every PHP matrix job.

Checked with this branch's own build-docker-compose-config.js: with WP_ENV_MARIADB_VERSION=10.5, docker compose config resolves the mysql service to mariadb:10.5 (and to mariadb:latest without it).

The other workflows (bundle-size.yml, create-block.yml, static-checks.yml) do not run wp-env.

Use of AI Tools

This PR was created by Claude Code under my supervision. All code should be treated as AI-produced and not yet reviewed by a human until this PR is marked Ready for Review.