[BUGFIX] Use correct date in rss

Change-Id: I807ef58e5967d49d2c0161d2957f004895239ad9
Resolves: #57167
Reviewed-on: https://review.typo3.org/28691
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer
(cherry picked from commit 00567689c2649337782c3ab469f07f3e7255b6f1)
Reviewed-on: https://review.typo3.org/28692