[BUGFIX] Add identifier to the file mount cache's value

This makes the groupHomePath and userHomePath features available
again.

Releases: main, 12.4
Resolves: #101188
Change-Id: I2d3ebc283b4ed72f0e2885c203c0ad2123c9a357
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79552


Tested-by: Benni Mack <benni@typo3.org>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Stig Nørgaard Færch <stigfaerch@gmail.com>