Mark libapparmor-perl Multi-Arch: same.
Thanks to the multiarch hinter for the suggestion. After reading https://wiki.debian.org/MultiArch/Hints#ma-same I confirm that the package only ships:
- architecture-dependent libraries under /usr/lib/$arch
- architecture-independent files in architecture-independent paths
… and includes no maintainer script.
So it should be safe to make it Multi-Arch: same.