test/images: bump agnhost, nginx, nginx-new, glibc-dns-testing for busybox 1.38.0-1

These Windows test images use busybox as their base image. Re-point their
Windows BASEIMAGE entries at busybox:1.38.0-1 (which adds --fqdn support to
hostname.exe) and bump each image version so the rebuilt images are published
and consumed by e2e:

  agnhost            2.66.0   -> 2.66.1
  nginx              1.27.0-1 -> 1.27.0-2
  nginx-new          1.28.0-1 -> 1.28.0-2
  glibc-dns-testing  2.1.0    -> 2.1.1