Revert "ci: Switch to crimson"

This reverts commit 0fe02db0.

.gitlab-ci.yml

-variables:
-    L5_DOCKER_IMAGE: pureos/pureos:landing
-
 include:
- - 'https://source.puri.sm/guido.gunther/librem5-ci/raw/master/librem5-pipeline-definitions.yml'
- - 'https://source.puri.sm/guido.gunther/librem5-ci/raw/master/pureos-packaging-ci.yml'
+ - 'https://source.puri.sm/Librem5/librem5-ci/raw/master/librem5-pipeline-definitions.yml'
+ - 'https://source.puri.sm/Librem5/librem5-ci/raw/master/librem5-pipeline-byzantium-jobs.yml'
+
+before_script:
+ - echo "deb http://repo.pureos.net/pureos landing main" >> /etc/apt/sources.list.d/landing.list
+ - apt-get update
 
 stages:
  - test
@@ -11,7 +12,7 @@ stages:
  - test-package
 
 shellcheck:
- image: $L5_DOCKER_IMAGE
+ image: debian:bullseye
  before_script:
     - echo
  tags: