d/binfmt-update-in: fix binfmt being called in containers (LP: #1840956)

Christian Ehrhardtrequested to merge
paelzer-guest/qemu:bug-1840956-fix-binfmt-usage-in-container-debian into debian-unstable

The old container check only covers LXD and a few others. Using systemd container detection allows us to "grow with it" as they will implement new container types as they become known. This way this fixes for example the postinst of qemu-user-static in WSL.

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