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
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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