[RELEASE] Release 12.4.3

This is the last EXT:powermail release before starting the
work for TYPO3 v13 compatibility.
But dont fear: The TYPO3 v12 compatible version has
full support (bugfixes and features).
For details see https://github.com/in2code-de/powermail/blob/typo3-v12/Documentation/DevelopmentModel.md
Information about the EAP: https://www.in2code.de/en/agency/typo3-extensions/early-access-program/