[BUGFIX] Lower log level of TSFE->set_no_cache in preview mode

If TSFE->set_no_cache is called, either a warning or a notice is triggered,
depending if a BE user is connected or not.
With this change, the preview mode will trigger a notice instead of a warning.

This restores the same behaviour than before #86002.

Resolves: #96306
Releases: main, 11.5, 10.4
Change-Id: I40b9b1d90d42f14de2977aca61c24a9fd698ced0
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72578


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>