bug#40832: Audacity does not work with PulseAudio

[Leo Famulari]

Since I can remember, Guix's Audacity doesn't work with PulseAudio on my
foreign distro (Debian).

Debian's Audacity does work correctly in this regard.

In practice, this means that I cannot play or record audio in Audacity
while any other application is using sound on the system. If I close or
stop those other applications, then Audacity is able to select the
'sysdefault' output sound device and can start working.

I found a few discussions about similar issues [0], and it seems that
Audacity needs alsa-plugins in order to make this work.

I tried installing Audacity along side alsa-plugins,
alsa-plugins:pulseaudio, and pulseaudio, as well as building with them
as dependencies, but it still didn't work.

[0] e.g. https://forum.audacityteam.org/viewtopic.php?t=89278