[TASK] Display ApacheThreadStackSize message correctly during installation

With this patch the html chars inside the
"ApacheThreadStackSize" flashmessage during the installation are displayed
correctly

Resolves: #83413
Releases: master
Change-Id: If49ea5cd96ca8c0ef005e7a23b917b44149a88cd
Reviewed-on: https://review.typo3.org/55198


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>