Backport: lava: Update QEmu audio option

Pipewire tests may fail due to audio timeouts as the emulated sound card doesn't seem to consume data.
Replace -soundhw hda option by a dummy backend that discards all outputs. This requests QEmu version > 4.

https://phabricator.apertis.org/T8436

Signed-off-by: Frédéric Danis frederic.danis@collabora.com