add privileged permission to build

[guangbochen]

Problem: CI failed on https://drone-publish.rancher.io/harvester/harvester-installer/1516/1/2 with

generating harvester install mode qcow
Formatting '/go/src/github.com/harvester/harvester-installer/dist/artifacts/harvester-master-amd64.raw', fmt=raw size=268435456000
Could not access KVM kernel module: No such file or directory
qemu-system-x86_64: failed to initialize kvm: No such file or directory
time="2023-07-07T03:27:11Z" level=fatal msg="exit status 1"

Solution: add privileged permission to build

Related Issue:

Test plan: