What would be a good way to preview PR changes?

I currently use the now-bot (from zeit.co) to deploy previews of Pull requests towards my project (Located here).

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.