docker: Add arm64 builds to Dockerfile and CI #830

Job	Run time
test (arch)	1m 1s
Check DockerHub secrets exist	1s
test (bookworm)	51s
test (trixie)	55s
Build Docker container	15m 5s
Run unit tests	1m 45s
recipes on nofakemachine	40s
templating on nofakemachine	34s
debian (amd64) on nofakemachine	1m 14s
recipes on qemu	48s
templating on qemu	45s
partitioning on qemu	1m 10s
msdos partitioning on qemu	55s
debian (amd64) on qemu	6m 34s
recipes on uml	46s
templating on uml	56s
partitioning on uml	58s
msdos partitioning on uml	1m 7s
debian (amd64) on uml	4m 53s
recipes on kvm	36s
templating on kvm	45s
partitioning on kvm	40s
msdos partitioning on kvm	39s
debian (amd64) on kvm	1m 8s
debian (arm64) on kvm	2m 21s
debian (armhf) on kvm	2m 18s
arch on kvm	1m 40s
apertis on kvm	2m 58s
allgreen	4s
Publish to GHCR	0s
Publish to DockerHub	0s
	54m 7s

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