[FEATURE] Update PHPUnit to version 4

Since unit tests of the Core work fine with phpunit 4.x,
we update the bundled PHPUnit to the current version.

Change-Id: I87013a5c276174ed8c8bc8e75932288ebae7040e
Resolves: #59797
Reviewed-on: https://review.typo3.org/31057
Reviewed-by: Oliver Klee
Tested-by: Oliver Klee
Tested-by: Philipp Gampe