cerbero ci: Make before_script wiping more thorough
Will avoid packaging errors due to the old package file still being around from a previous job, such as in:
https://gitlab.freedesktop.org/nirbheek/cerbero/-/jobs/4804147
Will avoid packaging errors due to the old package file still being around from a previous job, such as in:
https://gitlab.freedesktop.org/nirbheek/cerbero/-/jobs/4804147