Incorrect output selection on Raspberry Pi 4/400

While testing the Ubuntu desktop images for Raspberry Pi which now use pipewire, I ran into a couple of odd default audio selections: LP: #1993316, LP: #1993347.

On the Raspberry Pi 4 it's a mild annoyance: the audio jack is selected as the default output rather than the HDMI audio. However, on the Pi 400 (the keyboard-based model) it's a bit more serious as the audio jack doesn't exist on that board so the stack is selecting a non-existent output.

I'm unfortunately not yet familiar with the pipewire stack, but I'll try and add some more useful details once the madness of the release has calmed down!