As ftp is indirectly becoming deprecated and less "common" switch to http(s) and fallback to ftp. Use GitHub as primary site to offload upstream main site, fallback if that fails to main site and try https protocol before falling back to ftp. While at it remove unofficial mirrors.
Reported here: https://lists.freebsd.org/archives/freebsd-ports/2021-December/001153.html
PR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=260302 (maintainer timeout)