[TASK] Update phpunit to version 5.6

Change-Id: Ia6e671bb39db820a93f0a534e8a0bd05cf325b49
Resolves: #78176
Releases: master
Reviewed-on: https://review.typo3.org/50106


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>
Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>