tests/arm64-without-qemu-support: disable binfmt not by uninstalling but by writing to /proc/sys/fs/binfmt_misc/qemu-aarch64

Since 1:7.0+dfsg-3, binfmt.d from systemd is used as preferred
alternative to binfmt-support. And systemd does not provide an official
way to trigger binfmt (de)registration besides a reboot.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1012163

Since we also have binfmt-support installed, systemd and binfmt-support
work in parallel so this test becomes flaky and sometimes removing the
qemu packages would have the desired effect and sometimes not.

To make the test deterministic again, we explicitly disable emulation by
writing a 0 to /proc/sys/fs/binfmt_misc/qemu-aarch64

tests/arm64-without-qemu-support

@@ -5,7 +5,7 @@ if [ ! -e /mmdebstrap-testenv ]; then
 	echo "this test modifies the system and should only be run inside a container" >&2
 	exit 1
 fi
-apt-get remove --yes qemu-user-static binfmt-support qemu-user
+echo 0 > /proc/sys/fs/binfmt_misc/qemu-aarch64
 ret=0
 {{ CMD }} --mode={{ MODE }} --variant=apt --architectures=arm64 {{ DIST }} /tmp/debian-chroot.tar {{ MIRROR }} || ret=$?
 if [ "$ret" = 0 ]; then