[BUGFIX] Correct whitespace handling in alert-message

Resolves: #104523
Releases: main
Change-Id: Ia331af805a4837f227289319b44f4f911463299a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85724


Tested-by: Andreas Kienast <a.fernandez@scripting-base.de>
Tested-by: Benjamin Franzke <ben@bnf.dev>
Reviewed-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Andreas Kienast <a.fernandez@scripting-base.de>