[BUGFIX] Fix path when writing AdditionalConfiguration.php

Use the getAdditionalConfigurationFileLocation() method to
determine the path to the file.

Releases: master
Resolves: #86561
Change-Id: I61b52e8eeb99ab2575f75025712a17f4c8ea4a40
Reviewed-on: https://review.typo3.org/58571


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Tomas Norre Mikkelsen <tomasnorre@gmail.com>
Reviewed-by: Rune Piper <kontakt@runepiper.de>
Tested-by: Rune Piper <kontakt@runepiper.de>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: Susanne Moog <susanne.moog@typo3.org>
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>