Add `spice-vdagent` as dependency for `qemu-guest-agent`

Description:

Without spice-vdagent, qemu-guest-agent.service will not start, giving:

qemu-user-agent failed with result 'dependency'

Additional info:

• package version(s): qemu-guest-agent 9.2.0-2, spice-vdagent 0.22.1-4

Steps to reproduce:

1. install in guest qemu-guest-agent, it won't work, and when you try to start it manually, it will give an error