[BUGFIX] Do not require */ext to be writable in Composer Mode

Resolves: #81857
Releases: master
Change-Id: I2dc07e8ac23edad2c7bd4880c4fd12ebcf2e40d6
Reviewed-on: https://review.typo3.org/57772


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>