mpd: Update to 0.23.8

mpd: Update to 0.23.8

Full changelog since version 0.23.6:

ver 0.23.8 (2022/07/09)
* storage
  - curl: fix crash if web server does not understand WebDAV
* input
  - cdio_paranoia: fix crash if no drive was found
  - cdio_paranoia: faster cancellation
  - cdio_paranoia: don't scan for replay gain tags
  - pipewire: fix playback of very short tracks
  - pipewire: drop all buffers before manual song change
  - pipewire: fix stuttering after manual song change
  - snapcast: fix busy loop while paused
  - snapcast: fix stuttering after resuming playback
* mixer
  - better error messages
  - alsa: fix setting volume before playback starts
  - pipewire: fix crash bug
  - pipewire: fix volume change events with PipeWire 0.3.53
  - pipewire: don't force initial volume=100%
* support libfmt 9

ver 0.23.7 (2022/05/09)
* database
  - upnp: support pupnp 1.14
* decoder
  - ffmpeg: fix HLS seeking
  - opus: fix missing song length on high-latency files
* output
  - shout: require at least libshout 2.4.0
* mixer
  - pipewire: fix volume restore
  - software: update volume of disabled outputs
* support libiconv

Signed-off-by: Peter Müller <peter.mueller@ipfire.org>