golang-github-sigstore-timestamp-authority release 2.1.3-1 for unstable

[dgit please-upload source=golang-github-sigstore-timestamp-authority version=2.1.3-1]
[dgit distro=debian split --quilt=unapplied]
[dgit upstream-tag=v2.1.3 upstream=811e94a148b97b90c638f58224d70d59da0c8b55]