ci: dl-cache: pull before committing

Another build job might since have commited its dl-cache hence do a pull
before we commit our dl cache.

.gitlab-ci.yml

@@ -33,7 +33,7 @@ default:
     - git config --global user.name "FFS Buildbot"
     - mkdir -p ~/.ssh
     - cat gitlab-known-hosts >> ~/.ssh/known_hosts
-    - cd gluon/openwrt/dl && git add . && git commit -m "update DL cache" || true
+    - cd gluon/openwrt/dl && git pull && git add . && git commit -m "update DL cache" || true
     - git push || true
 
 generate_date: