upgrade 18.04 to 20.04 error

[robt4reed]

upgrade 18.04 to 20.04 received following error:

W: download is performed unsandboxed as root as file 'focal.tar.gz.gpg' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)

[dino99]

yeah, an old remainig apt/dpkg bug over years ;)