As per https://github.com/PrivateBin/PrivateBin/pull/843#issuecomment-939526915 Co-Authored-By: El RIDO <elrido@gmx.net>
Adds a simple CI for pushing the master branches changes to the php8 branch. Useful/discussed for https://github.com/PrivateBin/PrivateBin/issues/707