tests/avocado: update sunxi kernel from armbian to 6.6.16

tests/avocado: update sunxi kernel from armbian to 6.6.16

The Linux kernel 5.10.16 binary for sunxi has been removed from
apt.armbian.com. This means that the avocado tests for these machines
will be skipped (status CANCEL) if the old binary isn't present in
the avocado cache.

Update to 6.6.16, in the same way we did in commit e384db41d8661
when we moved to 5.10.16 in 2021.

Cc: qemu-stable@nongnu.org
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2284
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Strahinja Jankovic <strahinja.p.jankovic@gmail.com>
Reviewed-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Tested-by: Niek Linnenbank <nieklinnenbank@gmail.com>
Message-id: 20240415151845.1564201-1-peter.maydell@linaro.org