sysutils/istio: fix build on riscv64

Bump golang.org/x/sys dependency to a version recent enough
to support riscv64-freebsd.  Chase repository renames:

github.com/{go-redis/redis -> redis/go-redis}
github.com/{kubernetes-sigs/service-apis -> gateway-api}

Sponsored by:	Berliner Linux User Group e.V.
Approved by:	portmgr (build fix blanket)
Differential Revision: https://reviews.freebsd.org/D39161