Please verify that buster related suites are functional

[Niels Thykier <niels@thykier.net>]

Hi Security team and backports team,

According to the release team's checklist we have the following TODO for
you:

"""
Check with security team and backports team that it is possible to build
uploads for -security and -backports
"""

To our knowledge, the relevant suites have already been created
(#917537) and ask that you kindly smoke test them to ensure they work as
intended.

 * Please let us know when you have verified these relevant suites or if
   you have any issues with them.

Thanks,
~Niels