tests: drivers: virtualization: qemu_kvm_arm64.overlay: fix SPDX license

"UNLICENSED" is not a valid SPDX License Identifier. Remove it from the
list and just keep "Apache-2.0".

Fixes: #89413

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>
(cherry picked from commit b240f115)