Update auto-update.yml

fixing this https://github.com/umihico/docker-selenium-lambda/actions/runs/5032943744/jobs/9026860425#step:18:40

Author: umihico

.github/workflows/auto-update.yml

@@ -131,7 +131,7 @@ jobs:
           git commit -m "${TITLE}"
           git push --set-upstream origin $BRANCH
           gh pr create --body-file /tmp/body-text.txt --title "PR:${TITLE}"
-          gh pr merge --delete-branch --merge $BRANCH
+          gh pr merge --delete-branch --merge
           gh release create $BRANCH --notes-file /tmp/body-text.txt --title "${TITLE}"
         env:
           GH_TOKEN: ${{ github.token }}