[CI] Include zuul.d/jobs.yaml as a trigger for image jobs

Zuul ignored the reconfiguration of the job vars and did not run
the promotion job in https://review.opendev.org/c/nebulous/activemq/+/919799/4

Change-Id: I2e8a66bce1ae16cbeb5a12ec8e607e961ae8342f

zuul.d/jobs.yaml

@@ -8,6 +8,7 @@
       - nebulous-exn-middleware-container-images
     description: Build the container images.
     files: &image_files
+      - ^zuul\.d/jobs\.yaml$
       - ^exn-middleware-core
     vars: &image_vars
       promote_container_image_job: nebulous-exn-middleware-upload-container-images