The issue I currently face however is, that the now-bot triggers a new deploy on every single push towards any branch, including the gh-pages branch I have.
This causes unwanted extra-deploys and also errors because of things like the requirements.txt missing on the gh-pages branch.
From what I understand does zeit.co not offer a way right now, to ignore specific branches or to disable specific features.
I now search for a good alternative, no matter if app or GitHub Action. I basically want something that would build the site with the changes of the PR, deploy it somewhere and then return a preview-link to see the changes.
If that is in any way important: I use mkdocs, which has both a gh-deploy command (to push changes to the gh-pages branch) and a build command.
I currently use a GitHub Action to automatically push changes to the gh-pages branch, which works perfectly.