Impersonate the pull request author with a static {{ author }} bot account

Set any bot_account (or merge_bot_account / update_bot_account) to {{ author }} to act on behalf of the pull request’s author. Mergify now treats it as a static value rather than a Jinja2 template, so it works consistently across all actions and queue rules, and appears as a “Pull request author” choice in your configuration. Jinja2 templating in these fields is being deprecated in favor of this static form.