Doc block fixes

[escopecz]

Please be sure you are submitting this against the staging branch.

Q	A
Bug fix?	Y
New feature?	N
Automated tests included?	N
Related user documentation PR URL	/
Related developer documentation PR URL	/
Issues addressed (#s or URLs)	/
BC breaks?	N
Deprecations?	N

Description:

We've got PHPSTAN level 5 errors in our plugin which had to be fixed in Mautic itself. So here they are.

Parameter #2 $location of method Mautic\CoreBundle\Event\CustomButtonEvent::addButton() expects null,
Parameter #2 $channelId of method Mautic\CampaignBundle\Event\CampaignExecutionEvent::setChannel() expects null, int given
Parameter #3 $columnName of method Mautic\CoreBundle\Doctrine\Mapping\ClassMetadataBuilder::addNullableField() expects null, string given.
Parameter #3 $afterDate of method Mautic\CoreBundle\Model\AuditLogModel::getLogForObject() expects null, DateTime given.
Parameter #7 $entityIdColumnName of method MauticPlugin\CustomObjectsBundle\Controller\CustomItem\ContactListController::generateContactsGrid() expects null, string given.

Steps to test this PR:

1. There is no code change so this PR cannot break anything. Just method doc block changes. Code review is good enough.