fix: CI: debian: create the debian branch

.gitlab-ci.yml

@@ -12,6 +12,8 @@ debian:
     - apt-get install -y git-buildpackage lintian piuparts
 
     # Build the package
+    - git fetch --all
+    - git branch debian --track origin/debian
     - git checkout debian
     - gbp buildpackage --git-ignore-new