pkg-merge: Always submit a new MR, even with conflicts

Create a MR even when the local attempt to merge failed. In that case let the proposed updates branch point to the upstream branch and create a MR to submit it to the downstream branch.

This makes the failed updates more visbile and easier to track than the failed pipelines.

Task: T7797

.gitlab-ci.yml

@@ -29,7 +29,7 @@ before_script:
         RELEASE="${CI_COMMIT_BRANCH#*/}"
         TAG=latest
     else
-        TAG=$CI_COMMIT_REF_SLUG
+        TAG="latest"
     fi
     if [ "$STABLE" = "auto" ]
     then