misc/libpri: update to 1.6.1
ChangeLog: https://www.asterisk.org/asterisk-news/libpri-1-6-1-now-available/
- .github: Add Releaser workflow
- Link README to README.md
- Makefile: Fix modern compiler errors.
- Makefile: Add the ability to build libpri on MacOS for Linux target.
- q931.c: Fix subaddress finding octet 4.
Reported by: portscout