When you set up automatic publishing, GitHub will tell the publishing system when content within your repo has changed, and the publishing system will re-publish your book as necessary.
Set Which events would you like to trigger this webhook? to 'Let me select individual events' and select 'Pull request' and 'Push' (since these are the only events that should trigger an update)
When you set up automatic publishing, GitHub will tell the publishing system when content within your repo has changed, and the publishing system will re-publish your book as necessary.
https://docs.civicrm.org/mosaico/en/latest/