audio/praat: update to 6.4.23, latest upstream

As always, the release notes are at
https://www.fon.hum.uva.nl/praat/manual/What_s_new_.html
with some minor improvements.

While here, try to fix build on 15-CURRENT which is complaining
about typo's in uninstantiated templates. It builds for me,
but then I'm on 13-STABLE and therefore have a several-versions-older
C++ compiler.