debci-scheduler: APT configuration needs explicit setting of state file

When testing the upcoming debci-scheduler update, I received errors that a version for gcc-13 could not be found in stable. Which is correct, as stable still has gcc-12.

It turns out that when configuring python-apt for using a custom configuration director, it is insufficient to specify the Dir config option and assume that this is effective for all other settings in that namespace.

At least the Dir::State::status option has to be set explicitly, otherwise the system-wide /var/lig/dpkg/status is used. Which, in case of my tests, has information from unstable, which explains how gcc-13 landed there.