Fixes issues with the action that comments updates on merged release
PRs:
1. Multi-line LINKS_VALUE: Use '%s\n%s' command substitution instead of
literal newline
2. Heredoc delimiter: Changed to COMMENT_BODY_END_MARKER without quotes
3. Variable bug: Fixed incorrect variable (`$URL` not `$URL_TEMPLATE`)
4. Change from `printf` to `echo` (avoid weird printf gymnastics)
┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6663-ci-fix-action-that-comments-on-Release-PRs-2a96d73d365081b1b0c5c8e66f0e317f)
by [Unito](https://www.unito.io)
