For some unknown reasons it has been deactivated… I can also not reinstall it due this issue. No idea, but you can activate it again, if really needed:
sudo pacman-key --list-keys "ramon@manjaro.org"
sudo pacman-key --edit-key "77DC01C9971AC3C39A0626F72C089F09AC97B894"
gpg> enable
gpg> quit
Then it works again.