net/asterisk18: update to 18.26.1
Changelog:
https://downloads.asterisk.org/pub/telephony/asterisk/releases/ChangeLog-18.26.1.md
Security:
https://github.com/asterisk/asterisk/security/advisories/GHSA-33x6-fj46-6rfh
(cherry picked from commit 52c40397dd53d8b606b41f7d50fef201e4ad3207)