sound: test_pipewire_backend_invalid_stream panics with "Failed to connect to core: CreationFailed"

[epilys]

Test panics:

2024-04-09 12:11:58 EEST	failures:
2024-04-09 12:11:58 EEST	
2024-04-09 12:11:58 EEST	---- audio_backends::pipewire::tests::test_pipewire_backend_invalid_stream stdout ----
2024-04-09 12:11:58 EEST	INFO: dbus_session_bus_address=unix:path=/tmp/.tmpJ52ZlF/dbus
2024-04-09 12:11:58 EEST	INFO: Wait for dbus to setup...
2024-04-09 12:11:58 EEST	INFO: Launch pipewire.
2024-04-09 12:11:58 EEST	INFO: Wait for pipewire to setup...
2024-04-09 12:11:58 EEST	thread 'audio_backends::pipewire::tests::test_pipewire_backend_invalid_stream' panicked at vhost-device-sound/src/audio_backends/pipewire.rs:97:42:
2024-04-09 12:11:58 EEST	Failed to connect to core: CreationFailed
2024-04-09 12:11:58 EEST	INFO: Killing pipewire pid 4573
2024-04-09 12:11:58 EEST	ERROR: pipewire stderr [E][00324.655638] mod.rt       | [     module-rt.c:  236 pw_rtkit_bus_get()] Failed to connect to system bus: Failed to connect to socket /run/dbus/system_bus_socket: No such file or directory
2024-04-09 12:11:58 EEST	[W][00324.655651] mod.rt       | [     module-rt.c: 1055 pipewire__module_init()] Realtime scheduling disabled: unsufficient realtime privileges, Portal not found on session bus, and no system bus for RTKit: Connection refused
2024-04-09 12:11:58 EEST	[W][00324.658561] default      | [        thread.c:  101 impl_acquire_rt()] acquire_rt thread:0x763141eea640 prio:-1 not implemented
2024-04-09 12:11:58 EEST	
2024-04-09 12:11:58 EEST	INFO: Killing Dbus session 4415
2024-04-09 12:11:58 EEST	INFO: dbus stdout unix:path=/tmp/.tmpJ52ZlF/dbus,guid=e7164449469d64fe0d7646386615065c

From this CI run: (link may expire in the future)

https://buildkite.com/rust-vmm/vhost-device-ci/builds/2362#018ec21f-9400-4792-9cc7-0d3f336e7120