ci(magento): run the adapter integration tests (#738)

[gplanchat]

What

I add one step to magento-boot, after Psalm: it creates a durable_test database on the job's MySQL 8.4 service, grants it to the magento user, and runs vendor/bin/phpunit -c phpunit.magento.xml --display-skipped --fail-on-skipped with DURABLE_TEST_MYSQL=magento:magento@127.0.0.1:3306/durable_test.

The suites under tests/integration/DurableModule (resume lock, table queue, run projection) skip themselves unless magento/vendor exists and DURABLE_TEST_MYSQL names a server. No job set both, so merged code was never exercised. magento-boot has the Magento install (magento/vendor) and the root vendor/ (PHPUnit), and I give the tests a database of their own so they cannot touch the shop's tables. ci-ok already needs magento-boot, so its list does not change.

This does not close #738: the issue also asks for a second MySQL declared as db/connection/durable, durable:setup, the conformance harness under magento/ and the restart experiment. Those stay open.

Checked

• The YAML parses and the step sits in magento-boot.
• I could not run the job locally (it needs a Magento install, MySQL 8.4 and OpenSearch). This pull request is its test.
• Assumed: posix is available in the setup-php build (the lock tests kill a process), and the magento user may be granted a database by root.