.oniro-ci: skip build-doc job for scheduled pipeline as it runs when changes land

Signed-off-by: Chase Qi <chase.qi@linaro.org>

.oniro-ci/build-generic.yaml

@@ -436,6 +436,8 @@
     paths:
       - docs/build
   rules:
+    - if: '$CI_PIPELINE_SOURCE == "schedule"'
+      when: never
     # Build the docs when a merge request is created.
     - if: '$CI_PIPELINE_SOURCE == "merge_request_event"'
       changes: