[BUGFIX] phpunit: Update comparator from 1.2.2 to 1.2.4

Raising this indirect require-dev dependency fixes a
PHP 7.2 compatibility issue on core 7.6 branch:
"Declaration of DOMNodeComparator::assertEquals() must be
compatible with ..."

Change-Id: I1c422edab82250b51ae9a0cc268110c62977ee08
Resolves: #83195
Resolves: #83120
Releases: 7.6
Reviewed-on: https://review.typo3.org/54910


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>