Mk/Uses/go.mk: Set GO_NO_VENDOR_CHECKS=1

Set GO_NO_VENDOR_CHECKS=1 to signal lang/go to relax vendor checks during ports
build.

PR: 244783
Reported by: Christopher Hall <hsw@bitmark.com>
Reviewed by: mikael swills yuri
MFH: 2020Q2
Differential Revision: https://reviews.freebsd.org/D24122