Discrepancy of build options between debusine.debian.net and official buildd for experimental

For experimental, buildds use: --build-dep-resolver=aspcud --aspcud-criteria='-count(solution,APT-Release:=/experimental/),-removed,-changed,-new'

But on debusine.debian.net we use --build-dep-resolver=aptitude because we share that configuration with the backports suites.

We could create a new dedicated task-configuration collection to achieve this but I think we'll wait until we have a simpler way to manage those per-workflow tweaks (cf freexian-team/debusine#1231).