fix(service-project): Use `$CI_CONFIG_PATH` instead of hard-coding `.gitlab-ci.yml`.

ci-tasks/service-project/impl.yml

@@ -40,7 +40,7 @@ stages:
     - if: $CI_PIPELINE_SOURCE == 'merge_request_event'
       changes: &validate_changes
         - .runway/runway*.yml
-        - .gitlab-ci.yml
+        - $CI_CONFIG_PATH
         # Specific to AI Gateway
         - ci/gitlab-com.yml
     - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH