course/format/tests aren't executed ever

Was working on one more check to be added to CIs:

https://github.com/moodlehq/moodle-local_ci/pull/249

Because it's something we had in the past (as part of the phpunit execution) and because we have faced this same problem a number of times in the past.

And that new job is clearly saying us:

ERROR: course/format/tests is not matched/covered by any definition in phpunit.xml !

Looking to phpunit.xml, certainly there isn't any suite created for the tests under course/format/tests.

So we need to add that suite, verify that tests (that haven't been executed ever) are passing and backport to all the branches having that subsystem with tests (311 and up, if I'm not wrong).

Ciao