Synchronize release KEYS from "old" typo3.org

https://typo3.org/fileadmin/releases/KEYS should contain three keys (Release Team, Benni Mack, mine) and was available on "old" typo3.org. Please synchronize the file once again.

The KEYS collection is for instance referenced in https://docs.typo3.org/typo3cms/drafts/github/TYPO3Incubator/InfrastructureGuide/Releases/#public-keys