Upload and unblock request for buster

[Arnaud Rebillout <arnaud.rebillout@collabora.com>]

  Hey go team,

I have a bit of a technical question regarding the freeze. I need a Go
package (namely docker.io) to be accepted to buster. To this effect, I
followed the procedure, submitted a bug against release.debian.org, and
got the approval from the release team.

I was told to upload the new version to unstable, which I did.

But then, a developer from the release team rightfully observed:

  Your upload incorporated a newer version of golang-golang-x-sys in
unstable,
  which has changes that are not appropriate during the freeze. If you want
  docker.io to migrate, the changes in golang-golang-x-sys need to be
reverted.

Which is correct! If I upload a source package in unstable, then it's
built against the packages that are in unstable at the moment. And
indeed, right now in unstable we have "golang-golang-x-sys (=
0.0~git20190412.9773273-1)", while in testing we have
"golang-golang-x-sys (= 0.0~git20181228.9a3f9b0-1)".

So how exactly am I supposed to do here? It seems that I need to build
the package against testing, but when I upload a source package to
unstable, then it's built against unstable, I can't change that.

Cheers,

  Arnaud