ci: Move to trigger jobs instead of REST calls

The REST calls no longer work, returning error 422. Move to trigger
jobs which seems to have been fixed. The down side is that we looses
the ability to run against user matching cerbero branch.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/9224>

.gitlab-ci.yml

@@ -1075,37 +1075,48 @@ build documentation:
           - "subprojects/gstreamer/**/*"
           - "subprojects/gst-rtsp-server/**/*"
 
-# FIXME: Using trigger: causes permission issues, workaround using old REST API.
-# https://gitlab.com/gitlab-org/gitlab/-/issues/341737
+
+# FIXME: We used to automatically run against matching user branch
+# whever that branch existed.
+# See ci/gitlab/trigger_cerbero_pipline.py.
+.cerbero trigger changes: &cerbero_trigger_changes
+  changes:
+    paths:
+      - ".gitlab-ci.yml"
+      - "ci/gitlab/*.py"
+      - "subprojects/gst-devtools/**/*"
+      - "subprojects/gst-editing-services/**/*"
+      - "subprojects/gst-libav/**/*"
+      - "subprojects/gst-plugins-bad/**/*"
+      - "subprojects/gst-plugins-base/**/*"
+      - "subprojects/gst-plugins-good/**/*"
+      - "subprojects/gst-plugins-ugly/**/*"
+      - "subprojects/gst-python/**/*"
+      - "subprojects/gstreamer/**/*"
+      - "subprojects/gst-rtsp-server/**/*"
+      - "subprojects/gst-examples/**/*"
+
 cerbero trigger:
   stage: build
-  timeout: '4h'
-  tags:
-    - placeholder-job
-  image: python:alpine
+  trigger:
+    project: gstreamer/cerbero
+    branch: main
+    strategy: depend
   needs:
     - "trigger"
-  script:
-    - pip install python-gitlab
-    - python ci/gitlab/trigger_cerbero_pipeline.py
-
+  variables:
+    CI_GSTREAMER_PATH: '$CI_PROJECT_PATH'
+    CI_GSTREAMER_REF_NAME: '$CI_COMMIT_REF_NAME'
+    CI_GSTREAMER_TRIGGERED: 'true'
   rules:
     - if: '$MESON_COMMIT'
     # Never run post merge
     - if: '$CI_PROJECT_NAMESPACE == "gstreamer" && $CI_COMMIT_BRANCH == $GST_UPSTREAM_BRANCH'
       when: never
-    - changes:
-        paths:
-          - ".gitlab-ci.yml"
-          - "ci/gitlab/*.py"
-          - "subprojects/gst-devtools/**/*"
-          - "subprojects/gst-editing-services/**/*"
-          - "subprojects/gst-libav/**/*"
-          - "subprojects/gst-plugins-bad/**/*"
-          - "subprojects/gst-plugins-base/**/*"
-          - "subprojects/gst-plugins-good/**/*"
-          - "subprojects/gst-plugins-ugly/**/*"
-          - "subprojects/gst-python/**/*"
-          - "subprojects/gstreamer/**/*"
-          - "subprojects/gst-rtsp-server/**/*"
-          - "subprojects/gst-examples/**/*"
+    - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
+    # For merge reqest, we want to test user branch
+      <<: *cerbero_trigger_changes
+      variables:
+        CI_GSTREAMER_PATH: '$CI_MERGE_REQUEST_SOURCE_PROJECT_PATH'
+        CI_GSTREAMER_REF_NAME: '$CI_MERGE_REQUEST_SOURCE_BRANCH_NAME'
+    - <<: *cerbero_trigger_changes