Update CI config

.gitlab-ci.yml

-include: "https://git.autistici.org/ai3/build-deb/raw/master/ci-nextstable.yml"
+include: "https://git.autistici.org/ai3/build-deb/raw/master/ci-backports.yml"
 
-stages:
-  - test
-  - build_pkgsrc
-  - build_pkg
-  - upload_pkg
-
-build_pkgsrc:bullseye:
+pkg_src:
   only:
     - master