Testing upgrade.php

[keevan]

Would be super useful to have a check that tests the "upgrade" path.

This could be triggered when there are changes detected in db/upgrade.php, to avoid slowing down test times for non DB related upgrades.

This will catch any issues resulting from things such as incompatible DB queries that pop up across different DB engines (e.g. mysql vs postgres etc) that might not be thoroughly tested due to natural bias. A recent one was detected for excimer and raised by @x-iy via internal chat.

This should be resolved upstream in the main CI checker here - moodlehq/moodle-plugin-ci#180 , and in doing so, changes in upgrade.php would be checked to confirm it won't break during a real upgrade.