[TASK] Replace placeholders in phpstan configuration

The phpstan configuration documentation recommends to specify the
paths relative to the directory of the configuration file.

Thus using, currentWorkingDirectory (as current working directory)
is unnecessary and removed.

Resolves: #96163
Releases: main
Change-Id: I2b625f4722e1955b5928a22dbdd2b4aedf6daafe
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72709


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>