Run the local pipeline whenever the parent pipeline triggers it

By default pipelines do not run in Merge Request context, but that's exactly what the parent ci-package-builder pipeline is now doing.

Add a rule to run the local pipeline in whatever context the parent pipeline triggered it.

debian/apertis/local-gitlab-ci.yml

@@ -11,8 +11,4 @@ test:
       job: prepare-build-env
       artifacts: true
   rules:
-    - if: $CI_MERGE_REQUEST_ID
-      when: never
-    - if: $CI_COMMIT_BRANCH
-      when: on_success
-    - when: never
+    - when: on_success # run whenever the parent pipeline triggers this