Fix release cron job (#7095)

CI failed because $4 was unset. We explicitly check later if it is set
so this is intentional, we just need to actually get to that check and
not fail due to set -u.

changelog_begin
changelog_end

ci/cron/wednesday.yml

@@ -42,7 +42,7 @@ jobs:
           branch=$1
           title="$2"
           body="$3"
-          out=$4
+          out="${4:-}"
           git branch -D $branch || true
           git checkout -b $branch
           git add .