Most MediaWiki repositories now have a composer test. The PHPUnit tests already install the composer dev dependencies and thus we should be able to run composer test directly in the job that runs the PHPUnit tests.
Benefits:
- we stop triggering the composer tests extra jobs that consume instances
- if lint/style fails, the PHPUnit jobs are not run at all and feedback is given faster
Since some MediaWiki repositories might lack a composer.json or a test entry point, we would have to take that in account.