This package seems to have been removed from the Arch repo, and also the -git version in the AUR is broken. See:
https://aur.archlinux.org/cgit/aur.git/commit/?h=apper-git&id=b8056bad9ffa140b91b4c1bec7e6fd7758b02bb0
https://aur.archlinux.org/packages/apper-git
I’d remove it and repeat the update.
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