[TASK] Update Swiftmailer to 4.3.0

Fixes: #38145
Releases: 6.1
Change-Id: I4b07bba0c08a7a44e1f2871c2ad46f6bea2d64e7
Reviewed-on: https://review.typo3.org/16738
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn