generate-stackbrew-library.sh removes latest tags

[J0WI]

@tilosp this removed the latest, apache, fpm-alpine and fpm tags. This seems to happen because of the RC release. https://github.com/docker-library/official-images/pull/5276

[tilosp]

it happens if generate-stackbrew-library.sh is run after a new version is released but the repo is not yet updated by update.sh. It shouldn't be a huge problem because it will be back as soon as update.sh is run (See: https://github.com/docker-library/official-images/pull/5284).