Add Phpunit test to check Drush commands

Here's a patch which adds a new test file for drush. Also drush needs to be installed via a command in drupalci.yml. Also for good measure I added it into composer.json test requirements.

The new test should fail, because the fix for #3078674: Call to function runLightweightCron() on null in SchedulerCommands->cron() has not been committed yet (purposely to try this new phpunit test on drupal.org)

As expected the new Drush test failed with

Error: Call to a member function runLightweightCron() on null in Drupal\scheduler\Commands\SchedulerCommands->cron() (line 59 of /var/www/html/modules/contrib/scheduler/src/Commands/SchedulerCommands.php)

We also got the Rules test failures which are caused by patching composer.json - see #2985051: Patching composer.json shows we need to add module dependencies

Here's a patch with the cron drush fix from #3078674: Call to function runLightweightCron() on null in SchedulerCommands->cron()

Typo in composer.json

Now to see if it works with the composer change only and not the drupalci.yml commands to get drush.

So it works fine without the container command mentioned in https://git.drupalcode.org/project/devel/blob/HEAD/drupalci.yml
Seems like having require-dev drush is in the composer.json file is sufficient.

Added a second drush test, to check that the nodes are actually processed during the cron run.

Done.