Debci setup fails to build jessie

Since the removal of all non-LTS Jessie package from the archive buildd-jessie-proposed-updates is not updated any more. This is making debci build fail when trying to build a jessie lxc.

E: Release file for http://incoming.debian.org/debian-buildd/dists/buildd-jessie-proposed-updates/InRelease is expired (invalid since 69d 1h 21min 57s). Updates for this repository will not be applied.
I: apt-get update failed, let's wait some time and try again 
Hit http://incoming.debian.org buildd-jessie-proposed-updates InRelease
E: Release file for http://incoming.debian.org/debian-buildd/dists/buildd-jessie-proposed-updates/InRelease is expired (invalid since 69d 1h 22min 15s). Updates for this repository will not be applied.
I: apt-get update failed, let's wait some time and try again 

https://salsa.debian.org/salsa-ci-team/autopkgtest-lxc/-/jobs/188725

Are oldstable flavors supported? I'm sorry it's an issue and not a fix.