audio/opus: update to 1.4

This new release brings the following improvements:

• Improved tuning of the Opus in-band FEC (LBRR)
• Added an OPUS_SET_INBAND_FEC(2) option that turns on FEC, but does not force SILK mode (FEC will be disabled in CELT mode)
• Improved tuning and various fixes to DTX

PR: 270996