Fix missing test_builds

{{cookiecutter.project_slug}}/.gitlab-ci.yml

@@ -39,6 +39,8 @@ build lectures:
     - chmod 700 ~/.ssh
     - ssh-keyscan tnw-tn1.tudelft.net >> ~/.ssh/known_hosts
     - chmod 644 ~/.ssh/known_hosts
+    - mkdir -p test_builds
+    - "rsync -rv test_builds {{cookiecutter.project_slug}}@tnw-tn1.tudelft.net:"
   script:
     - "rsync -rv site/* {{cookiecutter.project_slug}}@tnw-tn1.tudelft.net:$DEPLOY_PATH"