wireguard: selftests: use acpi=off instead of -no-acpi for recent QEMU

QEMU 9.0 removed -no-acpi, in favor of machine properties, so update the
Makefile to use the correct QEMU invocation.

Cc: stable@vger.kernel.org
Fixes: b83fdcd9

 ("wireguard: selftests: use microvm on x86")
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Link: https://patch.msgid.link/20240704154517.1572127-2-Jason@zx2c4.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>