[DOCS] Fix title and code example of changelog

The code example was not rendered, since a empty
line was missing.

Additionally, the title has to start with "Important:".

Resolves: #97072
Related: #93635
Releases: main, 11.5
Change-Id: I85b53f8d2f89558300b6ea996e1ab1147a678a92
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/73756


Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>