rootfs/bin/caddy: Rebuild caddy binary with go1.19.5.

Fixes CVE-2022-^(41716,41717,41720) in go stdlib 1.19.^(2-4).
Because [quic-go is bound to a given go compiler version][1], cannot
currently build with go1.20. Crafted a build host with
go1.19.5-linux-amd64.

[1]: https://github.com/quic-go/quic-go/wiki/quic-go-and-Go-versions

Author: joshix