[BUGFIX] Change list of (dis)allowed file extensions to ul li

Resolves: #104065
Releases: main, 12.4
Change-Id: I48c121620bf84a9444ff3c9d79d1adfd1fa631f3
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84655


Tested-by: core-ci <typo3@b13.com>
Tested-by: Andreas Nedbal <andy@pixelde.su>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Michael Telgkamp <michael.telgkamp@mindscreen.de>
Reviewed-by: Andreas Nedbal <andy@pixelde.su>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Michael Telgkamp <michael.telgkamp@mindscreen.de>