[TASK] Update php-cs-fixer configuration to exclude _generated directory

Resolves: #86730
Releases: master, 8.7
Change-Id: I9e707e6d9c1305baa92b7f2c4c0f83bbeea52daa
Reviewed-on: https://review.typo3.org/58683


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>