[BUGFIX] Avoid ReferenceIndex->enableRuntimeCache() in EXT:impexp

enableRuntimeCache() has been deprecated with #93038, with
all calls being removed. #94772 re-introduced one case,
probably during rebasing.

Resolves: #95569
Related: #93038
Related: #94772
Releases: master
Change-Id: I5f072f85d5714496870a5fdbb4694fd3426a56a5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/71536


Tested-by: core-ci <typo3@b13.com>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Benni Mack <benni@typo3.org>