content/en/cgi: Fix paths in cgi-style.pl, man.cgi, and ports.cgi

Adjust paths to point at cgit.freebsd.org instead of svnweb.

An attempt has been made to provide the same kind of information as
before, but the layout and information displayed by cgit is different
from that of svnweb.

Reviewed by: wosch
PR: 255215
Differential Revision: https://reviews.freebsd.org/D29829