[TASK] NEWS.txt entry about extbase changed STI

Change-Id: I0409ff835f6fc6624b7d1205290f914469e33a21
Resolves: #45326
Related: #11021
Releases: 6.1
Reviewed-on: https://review.typo3.org/19331
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn