Error "Failed to compute dynamic data: get() returned more than one CollectionItem" with a sbuild task and some task configuration

The sbuild work requests in this workflow failed to be assigned a worker with:

2025-08-27 16:28:47,982 [scheduler/3058121/139873338077248] ERROR: Error assigning work request Worker/sbuild (150942): Failed to compute dynamic data: get() returned more than one CollectionItem -- it returned 2!

(this is the log on the server side, there's no attached traceback)

At that time, I had this task configuration in place (my goal was to test the task configuration feature): https://salsa.debian.org/freexian-team/debusine.debian.net/task-configuration-developers/-/blob/0c6af6abb2926956e91b8f05a544c846fcf4ee3a/sbuild.yaml

This was shortly after a first try with build_options (but it's not implemented and it failed with a validation error):

I dropped it given the problem it seemed to generate and I replaced it with something similar on hello and hello-debhelper, but there I did not get any error (except that the sbuild task doesn't like backend incus-lxc apparently):

/cc @enrico

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