www/ungoogled-chromium: update to 125.0.6422.76 and implement selectable audio backend support

with these changes, chromium now automatically selects which
audio backend to use in the following order:

pulse (if running) -> sndio -> alsa -> fake

an additional command line option has been also implemented so
that the user can force which backend to use:

--audio-backend={auto,sndio,pulse,alsa}

Security: https://vuxml.freebsd.org/freebsd/8247af0d-183b-11ef-9f97-a8a1599412c6.html