[BUGFIX] Do not render HTML in Install Tool's flash message

This patch avoids rendering HTML tags in the flash messages of changes
that may be stored in the input fields of "All configuration".

Resolves: #78308
Related: #73143
Releases: master
Change-Id: I8f9e83684198ede3386b879035220f4888ba6d98
Reviewed-on: https://review.typo3.org/50235


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Reviewed-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>