ports(7) freebsd-release manual page misdirects readers to use SVN

Spun off from discussion in IRC

https://man.freebsd.org/cgi/man.cgi?query=ports&sektion=7&manpath=freebsd-release describes use of Subversion, should be updated with regard to Git.

The reference to https://svn.freebsd.org/ports/head is inappropriate. https://svn.freebsd.org/ports/head/UPDATING is more than two years out of date, and so on.

https://man.freebsd.org/cgi/man.cgi?query=ports&sektion=7&manpath=FreeBSD+14.0-STABLE and https://man.freebsd.org/cgi/man.cgi?query=ports&sektion=7&manpath=FreeBSD+15.0-CURRENT are better, with reference to Git (instead of SVN), so:

• cherry picks might be found to resolve this issue.