fix head body payload

.forgejo/workflows/auto-update-pr.yaml

@@ -59,7 +59,7 @@ jobs:
             -d '{
               "title": "chore: weekly flake update ${DATE}",
               "body": "Automated flake update from CI",
-              "head": "'"${{ needs.prepare.outputs.branch_name }}"'",
+              "head": "'"${{ steps.commit.outputs.branch_name }}"'",
               "base": "master"
             }' \
             "${{ forgejo.api_url }}/repos/${{ forgejo.repository }}/pulls"