fix beta software warning

The cmake option should be set, overwise keepassxc thinks its a beta/snapshot software

https://github.com/keepassxreboot/keepassxc/blob/2.7.9/CMakeLists.txt#L159

https://github.com/keepassxreboot/keepassxc/blob/2.7.9/CMakeLists.txt#L128

https://github.com/keepassxreboot/keepassxc/blob/2.7.9/release-tool#L877