Using packages from another Salsa build (via aptly) no longer works

The documentation includes a method to allow one Salsa job to use binary packages from another package's Salsa build job. This no longer works: the first package creates the aptly repository, but the second package will not use it.

The first failure is that apt no longer accepts deb [trusted=yes] with no key. However, after working around that with

  - apt-get install curl
  - curl -o /etc/apt/keyrings/blockdiag.gpg https://salsa.debian.org/python-team/packages/blockdiag/-/jobs/8357955/artifacts/raw/aptly/public-key.gpg
  - echo "deb [signed-by=/etc/apt/keyrings/blockdiag.gpg] https://salsa.debian.org/python-team/packages/blockdiag/-/jobs/8357955/artifacts/raw/aptly unstable main" | tee /etc/apt/sources.list.d/blockdiag.list
  - apt-get update

it still fails because before_script runs before entering the sbuild chroot, which resets these settings.

If there is no easy way to actually fix this, I suggest removing it from the documentation.