Hi @samuelzeller,
google is indexing your site and is telling you, that that you blocked this url, because of the Disallow: /ghost/ statement in the robots.txt.
It’s not a problem per se and doesn’t need to be fixed. It won’t affect your website or proper crawling/indexing from google.
Those warnings are mentioned in the search console, so google can give you a notice, when you accidentally disallowed urls from indexing.
Usually you would fix that by adding a noindex meta tag to the according page.
Disallow: /ghost/ is supposed to be in your robots.txt, so that’s correct 