golang-github-sigstore-timestamp-authority release 2.1.2-1 for unstable

[dgit please-upload source=golang-github-sigstore-timestamp-authority version=2.1.2-1]
[dgit distro=debian split --quilt=unapplied]
[dgit upstream-tag=v2.1.2 upstream=21dff8b84c13344aa4a931d9779c514e4b7f8538]