Extend list of file changes for CI build of the haproxy image.

.gitlab-ci.yml

@@ -43,12 +43,16 @@ test:
   script:
     - make check
 
-# build new haproxy image if dockerfile changes
+# build new haproxy image after changes in: dockerfile, haproxy config,
+# exec script, or repo list
 build:haproxy:
   extends: .build-haproxy
   rules:
     - changes:
       - container/Dockerfile.haproxy
+      - container/haproxy.cfg
+      - container/haproxy_exec.sh
+      - container/buster-backports.list
 
 # haproxy image can be build when user triggers it
 build:haproxy:manual: