Setting up staging deployment on GL Pages?

Hi, we are building a static site and like it to be accessible on GL Pages.

We work on a dev branch for changes/modifications. Now, before we merge to master and then have the GL CI build the site and deploy to GL Pages, we like to access/view/test the changes/modifications from the dev branch also on GL Pages.

Currently, we encounter the issue that whenever whatever branch is deployed, all other artefacts (the actual files from other deployments beorehand) will get removed.

Any ideas appreciated. Thanks.